What Makes a Good Query Letter?
… You need a good hook, a succinct project description, a short bio and an explanation about why you’re the best person to write this book.
In addition, you need to present a case as to why this book needs to be published. Nonfiction is a harder sell these days than in the past because so much information is available for free on the Internet. We need to know why someone would buy your book rather than google your subject matter.