Approach your characters the same way. Over the course of a story, the protagonist's experiences will change his or her perspective, ideals, thoughts, beliefs, personality, etc. to some degree. Maybe it's something as simple as Edward discovering he can, after all, deliver a speech inf ront of the whole school. Or it could be as serious as Jess realizing she needs to let herself grieve for her mother. Whatever it is, your protagonist must change, someway, somehow.
Why? Because that's the whole reason you wrote your book.
Before you start pelting PM with rotten tomatoes for my presumptuous assumptions, let's work through this backward. The reason you wrote your book, the reason you write, is because you have something to say. A story to tell. A voice that won't get out of your head.
I believe a story is written to show to the world some kernel of truth you found, some irrefutable discovery that changes -- note the word -- the way you think, or feel, or perceive. And what other way to impart that feeling to your reader than through your own protagonist? To influence your reader, influence your character. And maybe we'll all experience something new.
