A friend of mine recently gave me a copy of Stephen King's On Writing. It's a fantastic read, giving insight into King's past and inspiration. It's also a wonderful tool for any writer, though especially for those whose goal it is to turn it into something more than just a hobby to be dabbled in every now and then.
As I finish up the first draft of my current project, I am gaining valuable insight from On Writing, and I only wish I had come across it earlier. It has excellent tips on how, when, and where to write, things to avoid in your writing, and even steps to take in the second and even third drafts of your books.
You don't have to be a Stephen King fan to read the book. You may despise his general work (which is ridiculous, 'cause he's The King). As he lays out his advice, he will admit his own faults and shortcomings over the years. I am a fan of King, but it is always encouraging to see a man as successful and prolific as him be humble and admit his own mistakes and shortcomings.