I don't usually use this blog to recommend books, but I just finished Orson Scott Card's How to Write Science Fiction & Fantasy. If you haven't read it, it's well worth the time.
Card deals with the specifics of writing speculative fiction, giving down-to-earth instruction and guidelines that will be helpful for the novice or seasoned writer. If you're like me, and have an interest in SF&F but have never written any, this book will open several worlds of possibility to you.
Even if you don't want to write speculative fiction, it may be worth the read to broaden your horizons and gain a few tips that will help you in other genres. You may find the brief section on the life and business of writing particularly helpful if you're a new writer. Regardless, it's an informative and entertaining read. Card is one of the stars of modern Sci-Fi writing, and when you read this book, you can see why.