Summaries are also called blurbs. The little paragraph on the back of the book or the inside flap that give a little more detail to the story’s premise. It is not a synopsis, which usually an extended summary of the story’s events, most often requested by a literary agent and a notorious bitch to write.
1. No climax or denoument necessary. Most summaries, like taglines or loglines, just build to the premise. They don’t tell how the premise ends (what’s the point of buying the book, otherwise?) Summaries should give context and world-details about the story in addition to the stakes of the story. So things like main character, the world he/she inhabits, and the problem he/she counters suddenly are all acceptable subject matter for a summary. Things that aren’t are deals like convoluted explanations for why story stakes matter, tertiary characters, political titles like Lord Chancellor Most Excellent, explanations of how magic or science mechanics work, or a list of the crazy or whimsical beings that hide within the pages. Sci-fi/fantasy terms should be used as sparingly as possible. For instance, I mention the Risen in my blurb, but only because they are a huge plot element in the story (and one of the main characters is a member of the race in question).
2. Context, please. The handling of exposition and emotional hooks is the real trick of a good summary. I see way too many blurbs that read like “A man struggles with heart disease! Oh, and there’s a werewolf.” A “WTF!?” reaction is not the same as “Hmmm, sounds intriguing.” Start with a variation on your pitch line or premise and build from there. After all, if you’ve reduced things to a single sentence, it doesn’t take much to unfold that little tidbit into a 3-5 sentence paragraph. (Yeah. That’s why I wrote about pitch lines first.)
3. Rewrite 3 times. At least. Too many people skip this step. To me, rewriting includes the “get critique” rule automatically. Considering the number of grammatically incorrect ebook blurbs I’ve read lately, this seriously needs to be said. If you’re paying no more attention to your ebook’s quality than you would a casual forum post, why do you honestly expect people to pay good money for it?
4. Don’t tell us it’s awesome. I hate seeing blurbs like “Your heart will pound as you read this fast-paced sci-fi yarn!” My initial reaction as a reader is “The hell you say, you narcissistic jackass!” The only people who are allowed to say a book was awesome or great is a book reviewer. A legitimate one, not a made up one. (Because that happens with ebooks and vanity stuff. Just ask Robert Stanek.) I realize this kind of stuff shows up in professionally published books, but it’s professionally published. It’s got some clout behind it. Stick to the story elements that are genuinely between the pages and leave the glowing reviews to the professional book reviewers.