Stephen King's On Writing: A Memoir of the Craft is the best book about writing that I've read. Several writer friends who I served on panels with recommended it to the audiences when they were asked what books have helped them. I hadn't read it, so I ordered a copy.
The book is frank, creative, and packed with real writing experiences and examples. It doesn't matter what genre you write.
These are my major take-aways:
1. "Good writing is often about letting go of fear and affectation."
2. "The best form of dialogue attribution is 'said.'" (Don't be creative with the attributions.)
3. "The road to Hell is paved with adverbs."
4. "I'm convinced that fear is the root of most bad writing."
5. "If you want to be a writer, you must do two things above all others. Read a lot and write a lot."
6. Turn off the TV. Get rid of the distractions.
7. Write everyday.
8. Research is "a specialized kind of back story." It belongs in the background.
If you're going to invest in books to help you improve your craft, this one needs to be in your library. And if I could only have one book about writing, this would be it.