I have an idea for a nonfiction book I want to write. What should I do first?
You don't have to write the manuscript for a nonfiction book before you query publishers. You can write a book proposal first. The book proposal is a very in-depth analysis of your book project, sometimes 100+ pages, that details the book's contents, the book's market or audience, and your qualifications to write the book and sell it. You also must explain how your book is different from or better than others that have been published on the same topic. The most comprehensive guide to writing a nonfiction book proposal is How to Write a Book Proposal, 3rd edition, by Michael Larsen.