Try these techniques to bring life to your characters, and find out who they really are.
1. Make a list of adjectives that describe your character. Use a thesaurus for words you may not think of off the top of your head.
2. Spend two hours "being" your character. Do whatever you are doing normally, but try to think like your character. Get inside his or her skin.
3. Write up questions and interview your character. Be "in character" when you answer.
4. Ask a friend or family member of the character to describe him or her, and write down the answers that come to you.
5. Describe your character on a typical day -- down to the underwear. Include hair, grooming, how long it takes him or her to pick out a pair of shoes. Everything!
Spend enough time with you character and he or she will be real, and that is how you want it to be for your readers.