What do you want? Chances are, you've got at least one answer to that question. Everyone wants something. That means your characters should, too.
Everyone has desires. It's a fact of the human condition that no matter what you've got, you want something else, or maybe something more. In order to make your characters real, they ought to long for something, many things even.
When I start a book, I always create a cast list (or character sheet) with basic descriptions of everybody. This is mostly so I can keep hair and eye color straight, but it is also useful for personality traits. Everyone has some desire, something pushing them to act as they do. Identify this in your characters and they will begin to come alive.
Real people have wants, wishes, desires. Real people yearn for things. They dream, they hope, they long. Incorporate desire into your character's personality, and it will be much easier for the real people reading your story to identify with it. If they can see themselves in any of your characters, you've done your job well.