From the various web sites I've visited, and from the info I've gathered from these boards, this is what I've learned about synopses (besides the fact that they're evil):
There's the one-page (single spaced), the short synopsis (3-5 pages, double-spaced), and the long synopsis (up to 10 pages double-spaced). Didn't find much info for the one-page variety. But for the other two, there was lots of advice. Both have a running header and page count, TNR preferred, paragraphs are not indented, but a space between each paragraph is required. Top left corner of the first page in both short and long synopses should contain the title, your name, genre, page count, and word count. Presumably they expect contact info on the cover letter or title page of your novel (unless they only request a synopsis, in which case I assume you'd include it under your name in the upper left corner of the first page). All three synopses are present tense and fast-paced.
The first paragraph should be your HOOK; that blurb that summarizes your premise and grabs the reader's interest. The other paragraphs should focus on major plotpoints only, while integrating major characters. More latitude is allowed with long synopses where subplots nad minor characters can be examined. Paragraphs should flow smoothly and logically into each other, and sound like a person telling a short story in first person. Major twists and the resolution need to be mentioned. Avoid open-ended questions like will she ever find him? Will he save the world? It was also recommeded that the synopsis be written in the same style as the novel to show the author's voice, but they caution against overdoing it.
Well, that's a summary of the info I've gathered together. I'm not claiming any of this is right, but I'm going with ideas that kept popping up. Find out what type of synopsis your agent/publisher requires, and you're off to a good start.
If anyone here sees glaring or even squinting errors in my info, please point it out as I can also use the advice.
good luck.