Okay, so you've written a compelling and convincing summary about your hero and heroine. You've presented motivation, goals, conflict for each. Shouldn't you be done?
Sadly, there's more torture on the horizon.
The next step to writing your synopsis is to describe the moment the hero and heroine meet, and not just the meeting, but the catalyst that brings them to that place. For example, if your heroine has been in too many bad relationships to count, has sworn off men, and avoids dating at all cost, how does she end up on a date with Mr-not-so-perfect, noticing his soulful blue eyes and charming grin? Did her best friend rope her into it? Is she a reporter on assignment? Did her mother's best friend's sister have a nephew in town for the weekend? If you're writing suspense or mystery, the meeting may be the result of whatever catalyst propels your characters into the story. One of my favorite yet-to-be-published manuscripts has a heroine seeking solace after finding her boyfriend in a compromising position. Where else to find comfort but an all-night bakery? Donuts. Yum. Unfortunately, she walks in on an assassin who's made shortwork of the gotta-make-the-donuts employee. The hero is an FBI agent who's taken a leave of absence to find his brother's killer. That killer is, of course, the assassin. She's a witness. He wants answers. And the story begins.
How does your story begin, and why is that beginning so important to your characters? What motivates them to seek each other's company, and what is going to keep them apart?
Once you've described the meeting, you're ready for my least favorite part of synopsis writing - chapter by chapter description of the plot. What this does not mean is excruciating detail of every moment of every chapter. What this does mean is touching on the highs and lows of the story. Think of your book as a series of mini black moments each followed by moments of realization. For example - the pastor who thinks his life is too full to ever consider romance meets a woman who has been in a series of bad relationships. Meeting her, talking to her, sparks something inside him - a realization that maybe he's more lonely than he cares to admit.
As you're writing your synopsis, focus on your characters' growth rather than the action. The formula for this is quite simple - she does such-and-such and realizes such-and-such. He responds by something which causes him to realize something. Eventually, these realizations lead them to their happy conclusion.
And lead us to the end of our synopsis.