Wordplay: Helping Writers Become Authors by K.M. Weiland. If you haven't visited her site, do so after reading this post. She also blogs on Authorculture, another fabulous blog for writers.
Visit her Popular Writing Tips page for info on everything from developing action in your novel to understanding theme.
She shares a wealth of knowledge on her blog so that other writers can become better at what they do. It's a site you'll return to. Trust me ;)