I'm no longer afraid of writing synopses.
This might be because I've written seven in the last year, at least. After about two or three, my attitude changed. I started worrying less and focused more on "knocking it out," telling myself I'd change things later.
You know, like you're supposed to when writing.
So there you go. My success tip for synopses. Write them really fast. Don't overthink them - all you need is to basically sketch out how the book follows a basic three-act structure. Don't worry about all of the crucial information you're leaving out (hint: you'd be surprised how much you don't really need). Don't worry about going to long or two short.
And remind yourself that everything - especially the book you're summarizing - can be changed. Just because something is in your synopsis, doesn't mean it has to be in the book.
The caveat to that is that the synopsis is what your publisher uses to write catalogue copy, possibly before you're done. So if you change things up, let them know. I was waffling about whether or not Sara went to visit her sister Rebecca for a while. The catalogue release sewed that one up.
So there you go. Happy synopsis writing!