I read somewhere once that a good practice when drawing a comic is to draw at least one foot per page. The idea is to break up the composition and keep from having page after page of talking heads. Of course, this not a hard and fast rule. Sometimes the story just doesn't allow for it, but I also think once per page is a lot. I went more for, like, every other page. Also, it's hard to draw someone puting on a bra and make it look half decent.