The characters are born from repetition, from repeatedly thinking about them. I have their outline in my head. I become the character and as the character I visit the locations of the story many, many times. Only after that I start drawing the character, but again I do it many, many times, over and over. And I only finish just before the deadline.
The trick to acting is not to show off; it's to think the thoughts of the character. I was lucky because when I started acting, it was doing jobs above pubs. I learned to act in anonymity, so by the time people saw me, I knew what I was doing. I was crap for years, but no one saw me being crap. It's a trade you learn.
Also, worldbuilding touches all aspects of your story. It touches plot and character as well. If you don't know the culture your character comes from, how can you know what he's really like? You must know your characters on a much deeper level than you would if you just shrugged your way into a cookie cutter fantasy world.
I am certain that I have been here as I am now a thousand times before, and I hope to return a thousand times. . . Man is a dialogue between nature and God. On other planets this dialogue will doubtless be of a higher and profounder character. What is lacking is Self-Knowledge. After that the rest will follow.