This book can help.
The Plot Outline Exercise is designed to help a writer work with a completed manuscript to identify and fix plot weaknesses. It can also be used to help flesh out an outline. Additional articles address specific plot challenges, such as getting off to a fast start, propping up a sagging middle, building to a climax, and improving your pacing. Guest authors share advice from their own years of experience.
Read the book straight through, study the index to find help with your current problem, or dip in and out randomly — however you use this book, you’ll find fascinating insights and detailed tips to help you build a stronger plot and become a better writer.