Sharlene Martin and Anthony Flacco, Publish Your Nonfiction Book.This book includes an outline for a book proposal and discussion of what works. There are many examples from successful proposals along with their analysis of what made the examples work.
Jane Friedman, The Business of Being a Writer. University of Chicago Press, March 16, 2018.This is a good source for checking expectations concerning what you can achieve as an author. How do some authors make money?