1. Don't write a summary.
Summaries are boring. Summaries don't catch your eye. Summaries don't make you take the book to the check out counter.
2. Imagine you are a news reporter.
What would your reporter see as news worthy? Murder, heroes, monsters. How would the ten o'clock news talk about such events.
3. Think about the headlines.
The headlines have to be eye catching. Pay attention to the blog titles, the magazine articles, the newspaper posts you read. Why did that headline catch your eye? What in your story deserves such a headline?
4. Practice writing headlines about mundane matters in your life.
Write a blurb, consisting of strung together headlines, about your new car, your kids, your spouse, your friends, your job, your grocery list. Hey, they make headlines for the supermarket ads!
5. Practice writing blurby reviews about the books you read.
Sometimes it is easier to see the headlines about somebody's else's work. So when you write a book review for your blog or for Goodreads, practice these blurby techniques.