According to August Birch, if you answer three magic questions your nonfiction will sell like hotcakes.
What’s a secret only I know about this subject? This is your Golden Goose. Your secret subject is the hook for your non-fiction. This is the insider’s bit of information and 98% of the reason your reader will buy your book. Most of you book is Google-able. But this — only you can provide the Golden Goose. Figure out this bit of information and release it carefully, deep into the book.
What are the basics my reader MUST know? This is the Google stuff. You’ve got to provide everything the lowest layperson must know to understand your book. Whether you’re teaching a skill, or discussing history, start at the beginning. You don’t have to cover it in-depth if you write an advanced book, but the basics need to be baked inside.
How can I arrange this book so it reads like fiction? You won’t bend the truth, but you can use narrative techniques (finish chapters with open-ended questions, later to be revealed) to keep the work moving. Don’t vomit all your best information up-front. Sprinkle it. Tell us you’ll reveal something important later, but not too soon. Arrange the book in a way that reads like a story. Non-fiction written by journalists are fantastic examples of this.