First thing you're going to need in order to participate in any action is a character, eh? You'll want to create a 'character concept' -- a one-line description of who or what your character is. It might include his/her race, temperament, fundamental ideals...
Expand on that. Create a 'profile' -- a brief summary that answers the question, 'What is the character like?' Gender, age, appearance, profession, fighting style, mannerisms, social attitude...
From there we go to abilities, and this involves a modicum of self-control. You want to avoid trying to make your 'perfect' character. We all know about our own real life inadequacies and imperfections -- don't try to overcome them by creating a flawless character! Character strengths need to be balanced by character weaknesses. This can be interpreted both physically (Bob the Brawny has huge muscles, but he's not quick or agile) and mentally (a street rat isn't going to have the social finesse of a noble). Sure, an all-powerful wizard would be fun and interesting for you to play, but not for the people playing the characters around him! And eventually, such a character wouldn't be challenging to play; just wave a hand and all his problems poof away. How much fun is that? In no time at all, you will soon discover that no one wants to play alongside a perfect character. Inevitably, they'll inherit an inferior role. Not even the badguys want to play opposite someone they can't possibly defeat. Most of the challenge in RPing is dealing with those flaws and watching the character grow.
There are, unfortunately, no hard and fast rules for Character Creation, but you'll want to make your character believable. Real people (and we'll use that term loosely!) are a mixed bag of good and bad traits. Give your character a weakness, a quirk, a bad habit! Don't cheat your character by letting RP situations impose characteristics. Here are some questions you might want to ask yourself when you're in the midst of your creating:
There is no requirement to start out with a fully-developed character. While it's not at all necessary to create an in-depth history and personality profile for your character, many players find it helpful to know the answers to some of these questions as they start to play a new character. The more you know, the better you are able to portray depth-of-character. As a result, you'll have a character that is interesting and engaging -- not just to you, but to other gamers.
Ready to go a little deeper? Consider the various aspects of these points:
Remember, too, that 'class' will have a major influence on all four of the previous points: A poor or lower-class family isn't going to have the same advantages as a middle-class family, nor will the middle-class family have the life of ease of an upper-class or noble family. While you're planning, remember to include high AND low points in your character's life.
And here's something to bake your noodle: It's a mistake to think that having a laundry list of your character's traits and habits is going to make him either believable or playable. It takes a while of hanging out in your character's skin to really get comfortable with him. So pull some of those notions out of the back corners of your mental closet, shake the dust off them, and come play!