Excellent information about writing your book proposal is provided by Rachel Toor. She is an associate professor of creative writing at Eastern Washington University's writing program in Spokane.
The Reality of Writing a Good Book Proposal, and the sequel, How to Write a Good Book Proposal, the Sequel, by Rachel Toor.
Her Web site is http://www.racheltoor.com. She welcomes comments and questions directed to firstname.lastname@example.org.