1. Relax. A synopsis alone will not make or break the sale of your book. Far more important is your author’s voice.
2. So don’t edit out your voice trying to keep a synopsis short. If the book is a romp, the synopsis should sound like a romp. If it's a gritty, dramatic tale, that should come across in the synopsis.
3. How do you get your voice in there? I write the first draft as if I’m sitting in a coffee shop telling the story to a friend. Although I write historicals, I’ll use modern slang or idioms or sentence construction. I can change all that later. But first, I’m just me, telling a story. When I’m editing, I’ll keep one or two sentences that sound most “like me.”
4. Concentrate on the moments when your main characters have to make key decisions. You might not be able to get every twist and turn of the plot in a short synopsis, so keep the focus on the major “make or break” moments.
5. Give one or two reasons from your character’s past to explain why they think and act as they do at those key moments. There’s no room for their life history, but we do need to know something of where they’re coming from to explain those major decisions.
6. Practice, practice, practice (or, if you’re Canadian or British – practise, practise, practise). Try writing synopses for your favorite books or movies. This can also help you understand why that particular story stood out for you.
7. Learn from the experts. Read reviews. Reviewers have a different agenda than an editor, but a good reviewer can certainly teach you how to describe a story in a short space.