Start writing the summary when you start reading the novel. As author Sheila Kelly suggests in "Writing the Novel Synopsis," jot down the characters, noting their motivations and conflicts, the setting, plot, sequence of events and theme or main point. (See Reference 1.) Add to these notes until you’ve finished the book.
Focus on the theme of the novel as you read each chapter. This trains your mind to pinpoint the essential details. For example, if a novel’s theme relates the horrors of war, you may not need to recall details of a character’s grade school education.
Summarize the novel in just one sentence by using your notes. You can do this by writing a sentence that answers the five W’s: who, what, where, when and why. For example, you might write: “An eager young soldier enlists to fight in World War II because he believes in his country’s cause.”
Build on that one-sentence summary, as Sheila Kelly explains. Expand the “who” element into several sentences or a short paragraph. Do the same with the other elements (what, where, when and why) until you’ve added enough details to aptly describe each. Some elements need more embellishment than others, depending on the novel’s theme. For example, if the story centers on the conflict between two characters, your summary should provide more details about each character’s personality and aspirations.
Keep dialog to a minimum, as advised by the Guide to Literary Agents (see Reference 2). Relying on dialogue is seen as an easy way out for writers who are content to let the story speak for itself rather than summarizing it. Use quotes only to support key points.
Consider how the novel’s theme helps the reader understand life in general. For example, if the novel portrays a character who separates himself from others who cannot accept his handicap, you might conclude the summary by pointing out how often people escape environments where they sense hostility.