Nobody likes writing synopses, in part because there is a natural desire on the part of writers to resist stripping their works of art down to the bare bones of plot points.
Writing a synopsis is also not particularly fun. If your strong suit is snappy dialogue or lyrical descriptions, you will be forced to leave all your little darlings behind.
The truth is you don't have to sacrifice creativity to write a synopsis, You can include descriptive adjectives and power verbs (avoid all forms of the verb "to be" and "to have" whenever possible). You can also include short dialogue if it is relevant to the plot.
How long is a synopsis?
Back in the day, synopses used to be quite long, roughly one page per every 25 pages of manuscript. (A 200-page book would have a synopsis of 8 pages.) But agents and editors are increasingly pressed for time, which means synopses have shrunk. The length now depends entirely on what the agent/editor requires.
It is a good idea to have several synopses on hand: a 3-5 paragraph synopsis (one page, or roughly 300 words), a 2-page synopsis, and a one-paragraph synopsis. Chances are the agent or house you are querying will ask for one of those.
Remember: A synopsis is a summary. It is designed to give an agent or editor a clear, concise idea of your story, not show your dexterity as a wordsmith.
Here are the basics for writing a synopsis
1) A synopsis must include all of your plot, including the ending. You can't end a synopsis with a cliffhanger or a question. "John dies" may seem like a spoiler, but that is exactly what an editor wants to know.
2) Be explicit. Details are important in a synopsis. A character should not experience "something unexpected." Say what that something is. For example,"The unexpected arrival of her father leaves Clarissa confused and angry." (It's important to include how your character feels. That provides a basis for motivation.)
3) Make sure your synopsis is structured. It must have a clear beginning, middle, and end, corresponding to the beginning, middle, and end of your book. The beginning introduces your characters, identifies the main conflict, and describes the setting. The middle outlines the main plot points. And the end resolves the conflict and tells us what happens to the characters.
4) Don't include too many twists and turns. It is not essential to include absolutely everything. If there are too many extraneous characters and subplots, it will be impossible to follow the story. Simplify wherever you can.
5) Make your synopsis stand out. If there is something unique about your story, make sure to give it the attention it deserves.
6) Write in present tense.
Before you start ...
It's a good idea to write a couple of synopses for books you did not write before you tackle your own. Like every other aspect of writing, synopsis writing is a skill, and all skills benefit from practice.
For a great list of synopsis examples, check out Writers Digest: Synopsis Writing