If you're a writer, you need this book.
Save the cat! changed my life. Before this book, I never plotted any of my novels. Needless to say, the logic was a mess.
Save the cat! is aimed at screenplay planning but it works just as well for novels and other stories. The website contains many examples of the 'Beat sheet' method popularised by this book.
Read it, understand it, use it. You need this in your library.
This book simplifies writing movie scripts and novels like nothing I've read before.