Anyway, here's a quote form their own description:
"99designs is the leading design contest marketplace, powered by a massive community of designers and contest holders."
1. I'm ready to win! (my folio says so... )
First of all, there's not much hope in winning a contest if you've been designing for about 1 week. If you're a webdesigner you need to have a folio of at least 30 creations before expecting to win a contest.
I will not talk about what should you design or what makes a good design. All I want to tell you about this is that an unique and professional design is really going to help.
2. Choosing the right contest.
The most important part is by far choosing your contest. If you're lucky you can find a contest having less than 3 designers participating (most of them having some "not-so-great" designs). But be careful, lots of these contests will be refunded due to the newly added "100% money-back guarantee" feature...
To have a greater chance of finding a contest in which a winner will be chosen you can look for 2 things:
a) Guaranteed contests (in these contests the CH must choose a winner, or the money will be split among all the designers who have entered the contest)
b) The CH has a "history of successful contests" (he held other contest in the past and choosed a winner).
The way I used to choose my contest was:
-> Selecting the design category I wanted (usually logo design)
-> Using the Search Filter to find only Blind&Guaranteed ones.
-> Aranging the contest by the "ends" column.
Here's another big decision you have to take: entering a blind or a normal contest. If you enter a normal contest you can see other's entries and understand better what the CH is looking for. The bad thing about this kind of contests is that your designing idea may be "stolen" by others that will tweak it a little bit and show proudly "their" great idea to the CH. You can report this to 99designs, but the chances for any actions to be taken are very small.
"So then, I'll just go for the blind ones..."
It isn't that simple. When entering a blind contest your idea will not be stolen, but the CH has to be very active. As a lot of 99d users said: "a blind contest without any feedback is a waste of time". It's true, if the CH only gives ratings and no feedback it's very hard to tell what exactly is he looking for. The good part is that a CH cannot launch a blind contest if he hadn't held any contests before.
4. When should I post my entry?
Things are really simple here:
If it's a blind contest you want to enter as soon as possible into the contest, so that the CH will have a lot of chances to give you feedback, and you'll have time to make all the changes he may want.
If it's a non-blind contest the best time to enter a contest is when less then 2 days have remained. This way others will not have time to copy your idea, but you'll still have time to receive feedback and make one or two revisions .
5. READ THE BRIEF!
Before even thinking about having an ideea for the contest make sure you have read the brief at least one time (that's why the "read the brief" button is before the "submit a design" one). If there's anything unclear about the brief feel free to send a PM to the CH and ask him to update it.
You must also read the comments the CH has posted in the "Discussion" board.
After you submit your entry you can either wait for some feedback & rating or you can just go and submit another design, improving your chances to receive some feedback on your entries.
6. I've received feedback!
This is some good news! Generally, when the CH gives you feedback means that he's interested in your designs. Don't stop here, try to have a conversation in the comment section and ask him what does he think about your designs, what should you change, what must be removed etc.
There can't exist a guide that tells you: "if you received 2 stars you should try a new design" or "if you receive 4 stars you should definitely tweak this same design until the CH likes it" . A thing you have to understand is that every CH has his own style of rating the designs. I've seen contests where great designs had 1 star (almost all designs in that contest had 1 star) and I've seen contests where even a paint-like entry had 5 stars (you should avoid these 2 types of contest). After receiving rating the first thing you should do is sort the contest entries by rating. This way you'll see how many entries are higher rated than yours.
8. Get your design noticed.
If you see that the CH feedbacks others' entires, but not yours, you can get your designs into his attention by sending him a PM asking him to have a look through your entires.
It's a bad idea to submit 10entries with the same design having only the colors changed. This will only make the CH think you're desperate and have no other ideas than the ones you've already submitted.
9. The CH chose my design as a winner!
Congrats! All you have to do know is go to the Design Handover page, transfer copyright, transfer all the files the CH needs and you're done. The money will appear into your 99designs account balance.
10. Never lose hope!
If you've entered a contest which made you think that you'll be the winner and the CH has chosen someone else don't stop trying. First of all designing is fun, and it's great to win money for "having fun". Also remember, it's freelancing: you can design whenever and whatever you want, you can also take a break when you feel you need to (e.g. 1week without opening PS or AI :) ).
As a fact, I used to work on 99designs too. My first win came along the contest #64. So I had to work on 63 contests before smelling the success. After that the wins came a lot easier. Until now I've entered 214 contest and won 6, I've also received about 4 projects outside the 99designs community from CHs, working directly with the client. I haven't entered a contest for a while but I have improved my working-style a lot so wins could come much faster. I've just taken one of those breaks...
Please ignore my bad English, I'm trying to get it better every day, but it will never be perfect :D .
Waiting for your comments!
99designs is posting a tutorial about using their search interface.
I have noticed that 99desgins changed it's contest system. I will update this post or make another one soon. :)