And lo, for the Gryphon returned from its abscence, and spake thus, saying "Y'know what? We should probably have a character creation guide." And thus it wrote, wielding keystrokes and Dead Fish of Smackage in synchrony.
Now with Deme edits, in italics, for extra hints, tips, and smackings. Why? I felt like it, is all.

Name: Something for us to call your character. Unicorns sometimes have a last name, usually a description or an epithet (Arem Taintblood, Cheka Rallsdaughter). Stuck? Try BehindTheName or Seventh Sanctum.
If you're really stuck on it, not even knowing where to start, move on and come back to it. Maybe something distinctive about your character will inspire a name. Also, although this isn't a rule...fwoofy names like (this is a REAL example) "Legendary Windsong" will earn you, if not an outright smack, glares for your entire tenure at this site, and beyond. These aren't prize racehorses. Try to make the occaisonal "secondary names" sensible, though. I'm getting really tired of random ones.

Breed: Has to be one of the six canon breeds, or a mixbreed. Sorry, no kirins or karkadons :/
There's also submitting a breed, but that's a long and arduous process. Best to save it for second, third, or fourth characters... This is a decision that ends up deciding a lot about your character, especially their rank and history.

Age: You'll want to see the breed descriptions for exact ages; assume that a 6 year old is a full adult.

Gender: Mare or stallion. I don't know why there would be unicorn geldings o____o
When you really look at it, there are more options such as intersex, etc, etc...if such a thing occours, also please put the sexual identity of said character. Also, there have been past cultures that have placed high value on the eunuch (none of the standard unicorn cultures do, though), so don't write of geldings, dear Gryphon. ^^

Ranks: What's your character's job or social standing?
Most ranks exist without requiring a herd. you can't join as one of the ones that requires a herd. also IF YOU CANNOT THINK OF A RANK, DO NOT PUT "NONE." YOU WILL BE SMACKED. the default for mares is "mare," the default for stallions is "stallion," and the default for foals is "foal." Try to branch out a little, too. Not every stallion has to be a warrior, etc. Variety = Fun.

Appearance: What does your character look like? We should be able to see them clearly. Are they tall or short for their breed? Are they built like a draft horse, or like a deer? What color is their coat (you can use natural or unnatural colors)? Is their hair coarse or silky? Any distinguishing scars or markings? What color are their eyes? Is their horn long or short, and is it blunt or sharpened? Do they have a beard or feathering? TELL US.
Oh, and please be creative. Jet black with red eyes/white with blue eyes and gold hooves = dead fish. Okapi or paint markings = cookie.
Looking at the breed's information helps, but remember: "usually" does not mean "always." Eventually, as soon as we have our mascots, I will start on new breed ref. sheets. And remember: Variety = fun.

Personality: Sentient beings are by nature multifaceted, but TRY not to make your full of contradictions. If you're totally stuck, try to consider their personality as a blend of two dominant traits (as an example, Cheka's are arrogance and rage). Is your character an introvert or an extrovert? Consider why they behave as they do. "Evil" and "nice" are not good descriptions of personality: "thoughtless" and "compassionate" are.
Don't give your character a psychiatric disorder unless you know all the symptoms and can play it. Jekyll and Hyde-ing between posts in a thread isn't gonna pull it for bipolar disorder.
Remember: your character does not have to be cold-and-arrogant OR uber-nice-and-happy. Variety = fun.

History: It's not that hard to write, dude. Where does your character come from? Did they grow up in a small herd or a large one? Were they raised by both parents? How were they treated as a child, and how did they learn their current job? How did they hear about the experient? Why did they leave their herd? It's generally more interesting if you leave out some details: it means we can stick more drama in the game.
If you say "she forgets" or "he does not wish to speak of it", I will SMACK YOU.
History is optional. If you don't want to put it up there, DON'T MAKE A SPACE FOR IT. While a good, well-written history does sweeten the deal for us, and is practically required for a fancier job/special breed/ a special adoptable, for something more mundane, it's not wholly nessicary. this rule was added practically because I didn't want to see "he/she doesn't speak of it." You character could be from SO many walks of life. remember... Variety = Fun. Are you brainwashed yet?

Miscellaneous Notes
Characters always end up better with a few flaws, be they physical or emotional. It adds a greater range of depth, and makes them far more believable.

They say your characters always end up like yourself. Having roleplayed hundreds of characters over the years, I'll say it's easier to play what you know, but it's definitely possible to play someone with a personality completely different from your own. They certainly don't have to be the same gender XD
And remember: have fun with it. Making a new character has always been one of my favorite things. You want to make a character that's good both ways: to play, and to play against. This will multiply the fun. We might eventually make a mary-sue test or an extra character creation help thead...possibly. You know, whatever.