Let me begin by being honest...even after writing 36 novels, I stink at writing synopsis. When I googled "dreaded synopsis" I got 1,430,000 hits. I think I can conclude that there are a lot of writers out there who hate writing synopsis.
In fact, if you want to make a lot of money-figure out how to write a good synopsis and then freelance out the service. A mere classified ad would do: "Need help with your synopsis? Synopsis guru will write it for you for $x..." It's money in the bank. LOL
I think the problem is that there really aren't any guidelines for synopsis-hints and tips, yes-but no guidelines. One agent only wants a back blurb like paragraph. An editor wants a one page synopsis. Another editor wants "no more than five pages." Wait- two pages are standard. No... rule of thumb is one page per every ten thousand words... Then there's a publisher-one I haven't ever been able to break into- who demands a "detailed" synopsis of indeterminate length as long as every emotion, subplot and turning point is in there...(they don't bulk at a 20 page synopsis and in fact would like more detail please...)
These many different vague demands of what the synopsis "should" be have spanned all kinds of classes and workshops on how to write a synopsis. Seriously- google it. The sad part is every single person will tell you theirs is "the correct way."
So- what is a writer to do?
I wish I had the answer. What I do is write several synopsis of varying lengths...then send them out with a wing and a prayer. Yes, so much for my "important selling tool."
That said here are some tips that I use in writing various size synopsis:
1) Start with the annotation or tag line-a fifteen word sentence that tells your story. Think NYT Bestseller blurb.
2) Write a back blurb copy for your story-three paragraphs that sell the story. (A good way to practice this is to go to Amazon or BN and copy some of your favorite author's back blurbs into a word file and then use them as a template for your own story. It's not cheating-it's called practicing.)
3) Write the goal/motivation/conflict for your main character. Then add in your story's turning points and the resolution.
4) keep everything in present tense.
5) Go online and read your targeted agent/editor/publisher's synopsis guidelines. FOLLOW THEM.
Keep in mind that no one really knows what a "good" synopsis looks like. It is as subjective as writing a "good" story. The best thing to do is relax. Give yourself a break and simply write it.