"Elements of Fiction Writing - Conflict and Suspense" by James Scott Bell
There are literally thousands of books on the craft of writing, and I've read my share of them. Some of them are good and they've helped me, but none as much as this one.
The problem with most writing books is that they are short and incomplete, but Mr. Bell's book is thorough in sharing tools and techniques for adding conflict and suspense to every element of your story, including characters, dialogue, and theme. So thorough, in fact, that as I was reading it, I kept thinking I was near the end because I had already read so much good stuff - surely there could not be more? But the author left nothing out. Mr. Bell goes over all the areas in a story and shows you how to inject suspense and tension into every scene. POV, Subplots, Openings, and Cliff-Hangers are also covered in the book.
When I am doing revisions, I keep this book at my side. I go through my work and use Mr. Bell's techniques on every page. And I can see the results. My dialogue, especially, has excelled. And that's why I recommend this book. As they say, the proof is in the pudding, right?
If you are going to buy one book on the subject of writing, this should be it. Mr. Bell's book is available at Amazon and also on iBooks.