So you want a character.
As pleasing as the idea might sound, it's generally a bad idea to just make up righteous and noble hero and rush onto an RP board. Creating a character for roleplaying purposes is the same as creating one for a book. Cliches won't go over well in either case. Take the time to think out a character before committing him/her to an RP. This page is designed to help you with the process of developing that character's personality and history, and will take you through it step-by-step.
First: Personality and History
Names, appearances, and species do not make a "person." The inner ideas and attitudes make a person. Therefore, whenever I am creating a new character, these two things are the first that I think about. The order that I think about them in varys, because the mind developes as its owner goes through various experiences. If I thought of an experiance first, I elaborate on that then think about how it would affect the character I have in my mind. If I think of a personality trait first, I think of a situation that might have made him be that way.
This is where cliches start to attack. Remember, you want to add some depth to your character. Try to answer these questions:
Another way to develop a character's backstory is to have one held very loosely in your mind and just set him loose. After awhile, a history might just come up to you and take you by surprise. My own experiances with this have been rather interesting, especially in regards to a character of mine named Geoffrey. Thanks to one line (it was, "Still trying to achieve immortality?" I believe) he was able to develop a full backstory and purpose for being.
Just remember the RP that your character is in, and the world that it is set in. Computers don't tie in very well in the Redwall universe, and swords and sorcery don't tie in very well in a futuristic type setting.
The best way to develope any character's personality is through roleplaying and/or writing that character. If you can truly allow yourself to be in that character's mindset, you can type something that will reveal a whole other part of his personality. It usually helps to think of your characters as fully different from yourself, and simply residing in your mind. The more you use a character, the easier it becomes to know just how he'd act in certain situations. So, really, just like anything else, RPing well and developing the personality of a certain character is practice more than anything else.