If you only get one how-to-write book, get Writing Love: Screenwriting Tricks II by Alexandra Sokoloff. (Okay, you could get Screenwriting Tricks for Authors instead, but there's all that and so much more in Writing Love.) Only $2.99 for the download.
This is the book I've been searching for. This book has answered my problems with plotting and character arcs. With this book, I will never again have to ask "What happens next?"
Just buy it already.
(Special thank you to Vicki Pettersson for sharing or I would still be stuck on what to write next.)