A book description has a different job from a plot summary. It helps a reader decide whether this is the experience they want. Begin by naming the kind of book you have written and the audience most likely to enjoy it. That private note will keep the public description focused.
Choose one central thread
For a novel, identify the main character, the disruption, and the difficult choice that follows. You do not need to introduce every important person. A list of names asks a browsing reader to memorize information before they have a reason to care.
For nonfiction, identify the reader's problem and the particular help your book offers. A memoir can foreground its setting, central tension, and emotional experience without claiming to solve the reader's life.
Make the stakes concrete
“Everything changes” is less useful than explaining what the character might lose. “Transform your writing” is less informative than describing the decisions or exercises the reader will encounter. Specificity gives your description shape without requiring exaggerated promises.
Fictional starting point: A retired teacher inherits a box of unsigned letters. To learn why her mother kept them, she must ask the one relative who refuses to discuss the past.
The example introduces a person, a discovery, and resistance. A finished description would also signal the novel's tone and expand the stakes without revealing the ending.
Cut the supporting machinery
Remove publication history, lengthy quotations, minor subplots, and explanations that belong elsewhere on the book page. Read the remaining text aloud. Does the first sentence give someone a foothold? Does each following sentence add something new?
Ask a reader unfamiliar with the manuscript what they think the book is about. If their answer differs sharply from the book you wrote, revise the promise rather than blaming the reader. Your description should attract people who will recognize the book they receive.