Laurie Hutzler breaks down characters according to 9 types. She has a free ebook and newsletter on her site. Her emphasis is on film and television, but characters are characters and this is one approach.

Another piece of advice is in the current issue of Poets & Writers magazine. Benjamin Percy discusses the Geometry of Dialogue, specifically giving your characters something to do when they’re talking. You will add layers to both your narrative and your dialogue. It’s worth checking out.