Characters and Viewpoint by Orson Scott Card
and The First Five Pages: A Writer's Guide to Staying Out of the Rejection Pile by Noah Lukeman.
I've read a bit of both books, and think that I'll start with Card. His first section, on "inventing" characters is about inventing/expanding both characters and plot. I'm hoping that this book will help me improve my characters before I complete the second draft of my novel.
I don't think I'll read the rest of the Lukeman book until I'm finished with this draft. Lukeman is an editor, an his book talks about all the things that might make him reject a book. I like the way this book is organized; in each chapter it starts with the problem, lists some solutions, shows some examples (although they seem exaggerated examples), and concludes with some exercises. I like the exercises, because they are generally meant to be tried out on your own manuscript.
I'm leaving this book until after the second draft is finished, however, because it is geared to editing and fixing problems... and not to writing. My second draft is about writing the new scenes for my book and rewriting existing scenes to work with the new plot.