sassandgroove said:
Might I be so bold as to suggest Orson Scott Card's book How to Write Science Fiction & Fantasy .
I love that book! My copy's got puppy teeth marks all over it.

I read it whenever I feel discouraged (in fact, I think it would make good bedtime reading tonight).
One of the things I keep remembering is Card's distinction between SF and fantasy--if it's got rivets, it's generally going to be perceived as SF. My book is set in the future in a large city, and in fact the climax happens on a terraformed Mars, so it's got rivets. But the main character is a dragon, although not a typical fantasy-type dragon. There's no magic in the book at all. I actually asked about the genre in a thread in the SF/fantasy forum the other week, but the answers were inconclusive. Penguins somehow took over the thread.
Anyway, I'm trying to think of legitimate subplots that I could introduce seamlessly without overwhelming the main plot or slowing the action. Unfortunately, I like to have my subplots tie up with my main story in the end, so adding a subplot (or two) now might easily change the entire book. Maybe that's what's needed, though. Unfortunately I really like it the way it is--but if it's not going to have a chance of selling as it is then I need to change it.