I was thinking about art books earlier. There are a lot of great how-to books on art. They cover drawing, painting, etc. Some that come to mind for comic book artists are Comics And Sequential Art by Will Eisner, How To Draw Comics The Marvel Way by Stan Lee and John Buscema, and any book by Christopher Hart. You can learn a lot about how to draw comics from those books. Those guys are experts, and they know a lot about how to draw comics.