Here's a tip/info i gleaned from the wonderful Michelle Styles:
There are five things you need to include in any synopsis
1. The setting -- specifically where does the action take place?
2. The main characters -- what are their major motivations or conflicts both externally and internally.
3. After the magic words, When the novels begins, you tell your main story. If this is a romance, you are telling of the growing attraction and the set backs the couple encounters on the way. If it is a saga, you are telling the story of one woman’s growth arc..
4. The Back Moment. -- how does the story reach its climatic moment, what happens
5. The Resolution, the happy ending. Tell the editor how the story ends.
Do you have any tips to add?