I find that I can only get to know a character when I start writing him or her. No matter how much I plan, write, or contemplate a character, they only come to life in my mind once they I have to animate them in scenes. Same with role-playing too. Now that doesn't mean that I don't write any background or notes, but those notes don't really match the product that characters will create in the story. That makes outlining a serious problem because the characters don't behave and do what I want them too.
How do you get to know your characters?
One tip I have is to associate an actor with that character so that you can better realize him or her. Put that picture in your Story Bible and have it there to help you when you are in the wilderness.