I was thinking about entering my WIP in a contest, and the directions say I can include a one-page synopsis. Sure, no problem. I wasn't dreading writing a synopsis at all, until everything I read on them told me to calm down. That's when I really started getting nervous.
Here's a collection of the web resources I discovered to aid the process.
Overcoming the Fear of Writing a Synopsis... by Vicki M. Taylor
Mastering the Dreaded Synopsis--Condensing Your Novel... by Lee Masterson
How to Write a Synopsis... by Nathan Bransford
How to Write a Synopsis (Thread from AW) (includes links to samples)
Now, since I'm one of those odd individuals who learns by writing, let me summarize what I have learned.
A synopsis is a shortened, condensed version of your story, from beginning to end. (Yes, even in a mystery, you need to give the ending away) It needs to be concise, yet entertaining. You need to measure each word carefully, yet convey your individual voice. And it must sell your story without sounding like a sales pitch. In other words, a synopsis is impossible.
Some general pointers included starting with a hook--something to draw your readers on and make them want to read more--hopefully at least the rest of your synopsis. When you introduce a new character by name, capitalize all the letters in his or her name. Don't use a hinky font or play games with your margins. And write in third-person, present tense. Other than that, the length and format requirements vary widely, almost to the point where you need to disregard all instructions entirely, except for the ones given by the person or agency asking for the synopsis. Which means you're probably going to have to write multiple synopses.
But here is what I included in my single-page, single-spaced synopsis:
The hook: The hook I chose for my cozy mystery was character-driven. The first sentence introduced the reader to my character:
WENDY GILMORE has enough to deal with: hot flashes, empty nest syndrome, and trying to keep everything running smoothly at the church her husband pastors.
I think this works. From it we get a hint that she is having some trouble dealing with things. We also know that she is menopausal (which hints at her age). Empty nest syndrome could imply that she is lonely or not sure what to do with herself--at a transitional point in her life. And we know that her husband is a pastor, and that she is involved, or perhaps over-involved in the ministry if she thinks it is her job to keep everything running smoothly.
The second sentence introduced the plot--a murder. The rest of the paragraph summarized the action of the first act of the mystery, and the paragraph ended with the first twist.
Each successive paragraph told the plot of an act, and ended with the twist that ended that act. Each closing sentence was written to try to draw the reader on to the next paragraph. I only included five names--all major players. There was a final short paragraph (one sentence) that covered the denouement.
I did take care to include motivations (Why was this preacher's wife involved in a murder investigation?) and I included the motivation of the killer (Why did he do it? How did he justify his actions?) within the action narrative. And the synopsis, while omitting important details, told the main story without eliciting a bunch of "Huh's?" from my beta readers.
I edited it, tightening it up, slashing unneeded modifiers and sprinkling in stronger verbs. The only thing I'm not sure about is whether I was able to capture the humorous tone of the work in my synopsis, although there were several attempts that hint at it. The single-page requirement really made that difficult.
But I've worried about that long enough. At some point you're going to have to consider yourself done.