By the end, you should be inside your character, actually operating from within somebody else, and knowing him pretty well, as that person knows himself or herself. You’re sort of a predator, an invader of people.
The characters are the most important part of the book. You need to think like the character as you're writing them. This brings me to an article I saw on writer's digest. There was a writer who was a theater actor and he was able to do his characters much more easily because they have been accustomed to be someone else everyday of their life. I think this is where my minor in Theater comes in handy.