Actions. Not thoughts, not personality profiles, or likes and dislikes–actions. Just like real people, actions make the character.
I am learning, as I write The Spider Witch, that the actions of my beloved main character are tied to my own actions. I imagine my main character to be feisty, courageous, adventurous, strong, and witty–but I am none of those. How do I create a character I do not understand? How do I think like her, so that she may act in a way I would never act?
Maybe acting classes would help here.