Sure! I guess my general advice on backgrounds would be, to think about what they're supposed to do in the story... The mood is really important. Comics don't have a soundtrack, or moving cinematography to convey emotion, so the look and feel of the backgrounds - especially the lighting - is very significant.
I have a small tutorial up on the dreamkeepers website, in 'Behind the Scenes - Chapter 5', on how I put a typical page together from start to finish. It's not highly in depth, but I hope it's somewhat useful! 8 ) -[link]