One of my long-time students asked a great question: how does a writer develop voice?
I wanted to make sure she was talking about the writer's voice. Because there are two kinds of voice in books: the voice of the narrative, the writer's unique authenticity, and the voice of the characters. They are very different in how they are found, developed, and realized on the page.
Writer's voice comes as a natural process of maturing in your writing--as you begin to recognize what makes your writing unique and different in style and texture, as you begin to let go the fear of needing to fit in or sound like another writer you've long admired. It takes time, for most of us.