Many books sell on the strength of their authors. Authors who are bestsellers have their names above any title, riding on the reputation and good regard for prior books. New authors can reach for this power too. It begins with your author's bio. That summary of your life is important for debut nonfiction writers, with special attention to memoir authors who enter the stage with narrative nonfiction.
Bios for nonfiction rely on everything you've accomplished and survived. Big-time memoir writers bring an audience that's easy to identify. Contributor to NPR, columnist for Atlantic Monthly, YouTube sensation: all point at an existing audience. If you've got none of that going for you, there's still goodness to broadcast in your bio. Think of the bio as a key part of your resume and you'll be on the right track.
Be specific whenever you can. Saying you've been in a grad student ambassadorship program is not as good as naming it. In journalism school, where I cut my teeth on nonfiction, the motto when dog bites man was, "Always get the name of the dog."
Choose your experiences in order of their relationship to your book. If you're a fiction writer, the bio can be harder. Mention experience in writing festivals and programs if you've got that. Your novelist bio might include an inspiration like family history (again, be specific when you can) or a career that helps make you an authority. One novelist making her debut out of my workshops had 20 years of work in the state's Attorney General's office. She wrote a thriller about a cold-case criminal.
You never want to make something up for a bio. Save that energy for the book. But find your inner swagger. The bio is the part of a book proposal or a query letter where you find ways to say, "I'm the best person to write this book."