Here, you can see what users just like you say they find helpful or harmful when reading or writing a profile. I will provide links to all opinions, but will highlight the most agreed upon tips for quick reference.

First, here are the links I am referencing if you choose to just read the posts rather than sift through the wiki.

The Golden Rules of Online Dating

Be attractive.
Don't be unattractive.

The biggest misconception people have with these rules is that they focus too much on a person's physical appearance. This is hardly the case. Dictionary.com defines 'attractive' as such:

providing pleasure or delight, especially in appearance or manner; pleasing; charming; alluring: an attractive personality.
arousing interest or engaging one's thought, consideration, etc.: an attractive idea; an attractive price.
having the quality of attracting.

The biggest takeaway of this is that attraction is not just aesthetic. A major proponent to attraction includes your personality and charm as well. The more you focus on what you're not or don't have, the harder it will be for people to see what you are or what you can bring to the table. Also, keep in mind that even the most physically attractive individuals can be more bland than boiled chicken, so take that opportunity to outshine them in more substantial areas people search for.

Show, not tell! You can say you're charming, witty, funny, sweet, shy, good at (insert hobby)...but if I don't see it in your profile or pictures, I won't believe you. So back whatever you say up with proof. If you're witty, throw in a couple quips. If you're a caring individual, state your volunteer efforts or give a heart-warming anecdote.
(New!) You are NOT entitled to anything! Regardless of what happens, regardless of how well or badly things are going, and regardless of any preconceived notion of status quo or social standard, you can NOT ever expect something or feel as if you have the right to something. No one owes you anything, nor do they have to explain their reasoning as to why they do what they do even if you're involved. It works both ways, so don't forget that you aren't obligated to cater to someone else and their demands either. It's the internet. Sometimes, we forget that. We tend to fantasize that we are in an area full of other individuals like ourselves just looking for that next social connection, and that we will treat each other like proper human beings. It's unfortunate that it doesn't work like that all the time. Mutual star ratings don't require a conversation. Initiated messages don't require a response. A rejection response doesn't require justification. Not talking anymore in any part of correspondence doesn't require closure. It can be tough to take emotionally sometimes, but demz da breakz. You'll emerge from the end a bigger person, and the next person that comes along will be thankful that you were still available for the picking.

Profile Structure Overall

DO

DO leave profile sections completely blank instead of putting something lazy or half-assed.
Since people only see the very beginning of your profile and messages, and only your first picture when they are looking at things associated with you, make sure your leading edge is sharp. Good first 180 characters of the message, good thumbnail, and good opening to each section whenever possible.
Do take advantage of the free advertising. Make an edit a day to push your profile to the activity feed and get in front of your target audience. Even a simple rephrasing does the trick.

DON'T

Don't allude to sexual acts. This includes mentioning you're good at giving backrubs or any other kind of massages or kisses or pleasing others. To the person reading your profile, you're a complete stranger. Not many folks are up for letting complete strangers touching them. Exceptions if you're strictly after casual sex.
Don't generalize or use vague descriptors. Don't "hang out;" do "mind-mesh with friends over a tall beer at the local pseudo-Irish pub." Don't say "I'm nerdy;" do say "My collection of Iron Man paraphernalia likely rivals what Stan Lee keeps in his vault."
DON'T say "under construction! Will add more soon!" I will not be coming back to get updates. What you have up now is what I see. Sit down and do it, update as you will, but saying this just makes me think you can't finish something. Everyone struggles with filling their profile out, this is a cop-out that makes you look worse rather than better.
DON'T BE SELF-DEPRECATING! You're trying to highlight your best qualities. Do not ruin it all by getting stuck on how uncool you are, or what you're bad at. These things will stick out and will carry a lot of weight compared to other things in your profile. Only the best users can get away with a deprecating quip from time to time, but most often than not, it's best to play it safe and not do it.
Don't talk about your past relationships in your profile.

Pictures

DO

From our very own /u/mattheikkila's OKCuTips: "Your first photo should either show how attractive you can be, or be interesting enough to compel those you’re interested in to click on it when it’s a little 60x60 pixel thumbnail. Picking an odd, silly, weird, or goofy picture is probably not the best choice. I personally will click on a profile only if there is a reasonable chance that they’re attractive, and I do this for 3 reasons: 1 is to save time, 2 is because it’s a dating site and I’m only going to consider someone I find attractive, and 3 is because I don’t want to unnecessarily give the message that I may be interested (by showing up in their visitor list) if I’m definitely not. Usually a face shot with good lighting, no bathroom shots, or self shots if you can help it. Also, you can help it. Do you have one friend? Do you or they have a camera or a camera phone?

Your second and third photos should be flattering, and one of the three should be a full body shot, because there’s no point in dealing with the embarrassment of finding out one of you even accidentally misrepresented what you look like in person."

Your first picture is the most important piece of the profile puzzle. It's the first thing people see when searching profiles, and can be the make-or-break decision in less than five seconds of someone knowing of your existence. So, DO pick your absolute best picture! It must have great lighting, great composure, high resolution, and most importantly your best features being the most prominent eye-catcher in the picture. Also, when cropping, make sure to capture that essence because your thumbnail is your representative on the site.
DO have a few pictures alone, and a few with other people. Having lots of one and very few of the other will give bad impressions of either being too anti-social and difficult to mesh with your match's friends, or too clung to your friends and activities to have time for a partner.
Do show variety. Different places, different times, different moods, different atmospheres, different poses and different facial expressions will do more to show how multi-faceted of a person you are than any amount of words you type out describing it.

DON'T

Don't overload on the selfies. Cell phone pictures taken by yourself are tiring and hardly do justice to your features. Use a higher quality camera when possible.
Don't use bad lighting and unflattering locations. The worst place to take a picture is a bathroom. However, it's the most common. Why? That's where the mirror is. This tends to go hand-in-hand with the self-shots because it's easier to pose when you can see your subject, which is you. Get outside when possible during the golden hours of the day. DON'T BE UGLY BY ACCIDENT!
Don't take your clothes off. If you're looking for a more substantial connection than sex, then attract users non-sexually. Shirtless pictures, underwear/swimsuits, and very revealing clothing will set a person's perspective of you, and they will then mainly see you as that type of person. Additionally, these pictures may deter other users looking for substance from messaging you because they see you as only looking for a shallow connection.

My Self-Summary

DO

Do try writing this section last. Use the freestyle nature of this section to fill in anything you feel you didn't get the chance to say in the rest of your profile.
Do focus on who you /are/. The things you /like/ and the things you /do/ belong in other sections. What is it these things are supposed to tell us about your character?
Edit weekly.

DON'T

Don't say you suck at self-summaries. Lots of people dislike trying to summarize their complicated personality into a couple of paragraphs in a way they're comfortable with. You probably don't want to be lumped in with lots of people.
Don't portray negativity or entitlement! This is supposed to be the hook to your profile and coming off as either of those will turn away tons of viewers. Nobody wants to be around a stuck up little brat.
Don't write out your whole goddamned life story.

What I'm doing with my life

DO

Do tell us what you /do/. This sounds silly except folks never do it. What do you do for money? What do you do for pleasure? What do you do in between? What would I see if I followed you around for a week?
Explain WHY you like doing things or have the goals you have.

DON'T

Don't say, "Livin' it."
Don't say what you aren't doing; say what you're working towards.
Don't follow on with something you mentioned in your self-summary. Doing so can very easily make it sound like that's the only thing in your life, even if you mention other things. Its easy to get labeled and trapped as "that person who won't shut up about Y".

I'm really good at...

DO

Do brag a little, but be prepared to back it up. At this age, you have to be awesome at something. Don't hesitate to own it.
Be good at what few others have written about. Listening? That's like every other person who says they're good at it. Whistling? Now we're talking! It doesn't even have to be a real talent. "Stumbling in my heels." is decent. Even "drunk texting" (or the opposite: not texting when drunk) in proper context could make someone laugh.

DON'T

Don't downplay your abilities or say you don't have any. If you can't think of anything good to put, leave the section blank.
Don't play up TOO much either. There is an acceptable window of confidence in one's ability. It's important to stay within that window and not go too high and reach the cockiness range. If you don't know if you've said too much, ask someone else. They'll be able to tell you what they feel when they read.
Don't say, "cuddling, listening, being a good friend, etc." or any other generalized and mundane skill (if you would even consider that a skill). To emphasize on "being a good friend" and phrases like that, are you looking for a friend? No? Then why brag about that as your only ability? Because more often than not, that's all you'll get.

The First things people usually notice about me

DO

DO ask random people on the street, "Hey, just now, what was the first thing you noticed about me? It's for research."
If you're not as bold or socially unabashed, do the same on Facebook.
Pick something unique. Or, pick something typical, but explain why it's unique. This section is prime retail for icebreakers and you should do what you can to highlight an asset that someone wouldn't be afraid to approach you about.

DON'T

Don't ask your reader (the match who is looking to find reasons to message or not to message you) to tell you.
Don't say "I dunno I've never asked" or "you'd have to ask someone else" or some variation; these are cliched.
Don't mention something you would be upset for someone pointing out or focusing on in person. For example, women, if you mention boobs or butt, your matches will most likely spend a little more time on those parts because you've now mentioned them so candidly. They feel it's ok because you are ok mentioning it.

Favorite books, movies, shows, music, and food

DO

Pick representatives of what you like, not everything you like. If you share a specific favorite movie, book, or musician with someone it is SUCH an easy conversation starter.
Don't simply list, add context in any way you can.
Keep it to a minimum. If it takes up more than a laptop's screen, it's too long.

DON'T

DON'T list everything you can think of; this is easy and gives you an illusion of progress in building your profile. A representative sample is fine, but keep it brief. Many people go way overboard on this section, and it becomes hard to read (and easy to skip).
Don't say "I love too many, so just ask," "I like all kinds" or anything along those lines. Even though you think you're saying a lot about yourself, you're really not saying anything at all.

Six things I could never do without

DO

DO read this question with an emphasis on the word I. The six things I could never do without. That is to say, approach the question as the things you, only you, uniquely you, couldn't live without. There are things that everyone couldn't live without, but that speaks nothing about who you are as an individual.
DO list intangible things if you want. It does not say "six possessions I could never do without."
Do feel free to explain why some of these things made your list. A hairbrush is just a hairbrush until you explain that your hair is an untamed beast and only the brush can bring it down. The brush has personality now.

DON'T

Don't take this question literally. We know you need food and air and potassium and family and friends. Be creative and give us something else.
Don't just rattle off a few items of yours close by. Give it some thought and come back if you have to.

I spend a lot of time thinking about

DO

DO list things that interest you, like details about your hobbies, future goals (but be specific about those goals, Don't just say "my future goals") and plans for the immediate future if they are interesting and would provide a good talking point for somebody to message you.
Take the opportunity to say something funny. Think about something that would make you laugh, then write it.

DON'T

Don't say, "lol a lot of things, just ask me."

On a typical Friday night, I am

DO

DO feel free to describe an ideal Friday night rather than a typical one.
If you work Fridays or Saturdays, talk about another day or night off. This question is not necessarily about Friday the day. It means "What do you do for fun?" It just so happens that a majority of people work weekdays, and Friday night is the opener to the week's end.

DON'T

Don't say "there's no typical Friday night." This might be true but you have to give your reader something concrete to relate with. Give a few examples of what non-typical means over this bore of a cliche. "Anything from nudging newly-hatched turtles towards the sea to feeding the homeless to shotgunning PBR at a sorority I don't even belong to" tells us more about you.
Also, don't say, "Out with friends, or at home with a glass of wine." Come on now, don't be a cliche.
Don't be a cliche. If that means you gotta brush this section off with a joke, do that. If that means you gotta be a bit more specific, do that.

(Editor's note: I want to state that these are direct quotes from users like yourself. But do you notice a pattern? AVOID CLICHES!)

The most private thing I'm willing to admit

DO (I forgot to ask, so no link. Sorry)

DO keep it light and fun.
DO allow it to be a little revealing of yourself, but without diving too deep too fast. Basically, this is where you can display a bit of humility. "I still sleep with a stuffed animal/blankie/nightlight" or "I can't whistle" are perfectly acceptable answers that are still unique.

DON'T (Again, forgot to ask)

DO NOT say under any circumstances, "I'm on this site" or any variant to admitting that you're using OKCupid or any other dating site. First, only other online daters are going to see this, so it's obviously not a secret to them. Secondly, by saying this, you're being patronizing to the site and its users by showing shame that you've "stooped this low" to find a partner. People use this medium for a plethora of reasons, of which may not include desperation. It's insulting and offending to readers.
Don't say "I'm not telling here." First, the question isn't phrased "most private thing." It's the most private thing you're willing to admit. By stating that you're not going to say it not only demonstrates your lack of reading comprehension, but also gives the impression that you may be a secretive and prudish individual.
Don't go too deep. Everyone has their issues and skeletons in the closet. However, before even talking to someone, there is no need to open the door and let them see your darkest secrets. Just stick to something that would make for a decent icebreaker and leave the heavy stuff in the closet for another day.

You should message me if...

DO

Do focus on what you want out of the site. Ask for what you want. You want a hiking partner? "If you know any decent hiking trails in the area, preferably sans bears" can get those out. A multiplayer buddy? "If you've prestiged at least twice in the last Black Ops" alludes to that.
Put one last joke in there to round out your profile. At least something to put a smile on their face.

DON'T

Don't say "if you want to."
Don't use this section to compliment yourself. For some reason I see tons of guys put stuff like: "If you're interested in getting to know a cool, funny, good looking, intelligent guy." Prove to me that you're cool, funny, good looking and intelligent. It's tacky to say it about yourself.
Don't put a laundry list of requirements you do or don't want in a date (The people you're trying to avoid will still message you; you might as well say "don't message me if you didn't read this"...and the people you're trying to attract may be put off by what seems like a demanding person who has expectations and entitlement issues.) If you really have so many suitors that you must pre exclude people, frame it positively and keep it general. Instead of saying "no short guys," or "only if you're above 6'11"," say "I love tall guys." However, avoid usage of this completely if you can.

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For Messages

Source: Reddit (defunct)

Here is yet another section built by users just like you! Here are the most popular do's and don'ts, but you can find all the suggestions in the following posts:

/u/StevenMC19 asks reddit their do's and don'ts to messaging.

u/deleted offers their guide to messaging tips and opens the floor to commenters.

The Initiating Message

DO

Keep it light.
Be interesting in the first 100 characters. This is important because the introduction is visible before the message is even opened.
Keep it short. 2-4 sentences is an acceptable length. Be aware that you're not the only message in their inbox, and lengthy messages can get skimmed or skipped.
Show interest in getting to know them vs. smalltalk
Demonstrate that you've read their profile
Attempt to ask a question they haven't heard before. If not, dive a bit deeper into a topic they probably get quite often.
Use correct spelling, grammar and punctuation.
Imagine yourself talking to this person in real life. Don't write anything you wouldn't say to their face. Don't write anything that sounds too obvious or stupid.
Only initiate conversations you WANT to have. Don't ask someone about his/her interest in a topic just because (s)he's cute. If nothing interests you personally, let it go.

DON'T

Write just "hi, hello, hey there, etc." and expect to get a response. /u/Lachryman says, "I say 'Hey' to my coworkers every morning. I'm not trying to date any of them."
Copy/paste. For the love of all that is wonderful in this world, please put forth some effort if you're trying to find someone to be with.
Say "why don't you have a BF/GF? You're too attractive to be single."
Send any kind of first message that you wouldn't feel comfortable saying to someone in public.
Spend a bunch of time to introduce yourself, tell your life story, or explain why you don't think the person will message you back.
Mention how attractive you think he/she is in an opening message.
Open all possible topics of conversation or ask lots of questions in one question. Let the conversation flow and ask new questions in a lull.
Invest too heavily in a profile or message. It will hurt more if they never respond.
Be afraid to ask me out during our first or second message.
Give a fuck.
Mention sex for a while.
Neg, belittle, or clearly offend. (For those that don't know, negging is the practice of offering a backhanded compliment through a method of a borderline insult, or "Low-grade insults meant to undermine the self-confidence of another individual so they might be more vulnerable to your advances and seek your approval.")

Replying and Continuing Conversation

DO

Suggest a date early on in correspondence. Remember where you are. This isn't a chat site, but a dating site.
Adjust message length and tone to mirror what you're replying to.
Save some topics for the date. No need to know everything before meeting.
Respond when you want, and not after an arbitrary amount of time has passed based on some metric for what won't seem "desperate."

DON'T

Send a second message if they don't reply to the first unless your second message is asking them out, or you forgot to mention something and it's immediately after you hit send. (General rule of thumb...if you're not sure if you should or not...don't)
Get overzealous when setting up a date.

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Dating ProTips

Source: Reddit

This...

This is our Everest. This is our Mecca. We have made it to our destination and finally found someone to go on a date! Now...what do to...

Again, thanks to users such as yourself, we have created a list of dating protips as well a some do's and don'ts for you to utilize if you choose to make your dating experience more fun, efficient, effective, successful, and most importantly, safe.

Before the Date

Google Voice. Set up a number with Google Voice and never have to worry about strangers getting your real number again. Once set up, you can text, call and receive voice mails through the intermediary number (the only thing you can't do is send or receive pictures; sorry, dick pics). If someone starts to become an issue, you can go in and block that person's number, and they will not be able to contact you again. This works great with clingers and creepers.
Don't be afraid to Google your date. Knowledge is power, and what better way to know what you're getting into than to see if you can find their Facebook, twitter, or other social site they frequent just to get a peek into the type of person they are. Additionally, there is a predator alert scipt you can download which will detect the probability of a potential predator based on their own OKCupid.com questions answered!
Let someone close know you're going on a date. With who, where, when, and how long. Setting up a contact in case of an emergency will help if something happens and you need help from a trustworthy person.
Arrange to meet somewhere in public. If at all possible, meet there first, meaning do not accept a ride from them or offer them a ride. If an issue arises during the date and you've shared transportation, you won't be able to promptly leave and will be tethered to them until either you or they are home. Arranging a public meetup with respective methods of transportation allows the convenience of shutting down the date at any time.
BRING MONEY! You never know when your date may stiff on the check, or not have the cash necessary to cover their portion (or all) of the bill. For that, you'll need to be able to take care of it. It's an unfortunate truth that people are unprepared or simply want a free meal or drinks. It's up to you to watch out for yourself in these situations.
Confirm plans the day of the date. Make contact with your date and make sure it's still on. Maybe this person over-scheduled, forgot, or simply lost interest and is going to flake/stand you up. The last thing you want to do is to find out AT the date. Cement those plans and hop in the shower already! You've got a date to get to!

During the Date

Arrive on time or 5 minutes early. It's just a courtesy, and being punctual lets them know that you gave them your full time and attention.
Let them know you're running late. It happens. You had to stop for gas. Sir Reginald Poops-a-Lot struck again on the living room carpet not five seconds after you let him back inside. Mom wouldn't shut up on the phone while you were trying to get ready. We all know the usual hindrances. You just need to let your date know that it'll be another ten minutes or so later than you expected and that you appreciate their patience. You don't want them leaving before you get there, then you BOTH think you got stood up.
Keep in touch with your contact. Check in periodically to keep them informed and relieved. Also, if plans change, relay the details immediately. If your date has a problem with you checking in on your phone during the date even after you've informed them why, then so be it. Safety before rudeness.
DO NOT LEAVE A DRINK UNATTENDED! While it might not be in your mind at the time, and that this isn't just exclusive to online dating, it is important to remind you that the realities of date rape do exist. Driving separately and having a contact are two measures to prevent an occurrence, but those won't be much help if you aren't able to control your own body. PLEASE pay attention to what you eat and drink, and make sure the drink never left your eyesight.

Optional

Offer to split/pay the checks. This is more of a courtesy than anything. It is then up to your partner to agree to let you pay the amount you've requested, or to give them the chance to offer a rebuttal and pay their requested amount.
Lay out plans for a second date. If you have an interest with your date, it's always good to try and set something up while face-to-face with him/her. Actually schedule something, and not resort to the "we should get together again sometime" nonsense. If you throw out a location as well as a time and date, you can gauge your date's reaction based on it to determine their level of interest. Even if something doesn't work for him/her, an alternate idea will be presented. If not, this person may not express the same level of interest (or maybe they do; that's a gray area).

Date Ideas

The list actually grew quite large, so I had to make a separate page just for it. Here you go.

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