The characters in your novel have a heavy responsibility. They have to come up with witty dialogue, have interesting lives, and make snap decisions in difficult situations--all while looking fairly good and carrying the story. I don't think I'd want to trade places with mine!
To make characters that are more than cardboard thin, you have to get to know them. One way is to fill out any number of character questionnaires. Completing the exercises in Donald Maass' Fire in Fiction is also highly recommended (and I'll get to take his workshops again at a writing conference this spring!).
But I stumbled on another way to go deeper with your character. Take a personality test in their name. I got the idea from Fae Rowan over at Writers in the Storm. Her post, Meyers-Briggs: a tool for authors and other humans, details using a psychological survey on your character, and how to analyze the results. She even has a link to a free online test you can use.
Anything that helps a writer deepen their knowledge of their characters is a plus.
And now, just for fun, here are some questionnaires for you. Pick your favorite and find out more about yourself:
Did you find out anything fun about yourself? Have you ever given your character a questionnaire?