Rob Fitzpatrick's Write Useful Books is a guide to writing and publishing non-fiction. Fitzpatrick emphasizes creating highly useful books that readers will recommend organically, minimizing the need for extensive marketing. The book details a process involving early reader feedback to improve the book's structure and content before writing the manuscript. Key concepts include defining a clear book promise, ensuring effectiveness, and creating an engaging reader experience through strategic pacing of information. Fitzpatrick also discusses various marketing strategies, including leveraging podcasts, Amazon ads, and building an author platform.