Leave out ALL subplots. I had to physically empty my mind of everything but my two main characters. When I thought in these terms, it was much easier to know what to include and what not to include in the actual synopsis.
When you focus your synopsis just around the two main characters you can accomplish and share much more. What is their spiritual journey and show that as best you can throughout as you explain their growth. I usually culminate the spiritual growth at the end of the synopsis when I bring everything into a tidy package ending.
Pick two to three main points for each of your characters and include a couple sentences about it. How I typically lay out my synopsis beginning is:
Adelaide Proctor-Smythe is a hopeless romantic with the dress and the dreams…and one problem: she hasn’t a clue who the groom is. But until then, she’ll continue reading about romance and trying on “her” perfect wedding dress, hidden in the corner of Aunt Sissy’s Boutique. Addi might be in love with love, but when none of the guys in her hometown give her a second glance, something has to change. She’s determined to control her chance at love, but managing her destiny isn’t so easy when a “little head cold” becomes something more serious.
Levi Shraven has always loved one girl; problem is that “one girl” doesn’t know he exists. It’s a little hard to tell her, standing over a truck, elbow deep in grease, watching her in that white dress night after night. When he finds out Addi might be sicker than an antibiotic can cure, he can’t run out of time like when his mom died. Addi’s determination to change her life doesn’t seem to include him. Especially when she isn’t realizing he wants to take care of her for the rest of their lives.
Introduce both characters and their homeworld/goals. You're going to show through the synopsis the one thing the characters could do at the end that they couldn't do at the beginning. This needs to be a tangible action so the reader sees the change that has been happening within the heart of the characters.
With this latest synopsis I wrote, I intertwined more of the characters and their intersection throughout the story into the actual synopsis. Instead of breaking off "his" and "her" lives and making everything the other character did in a separate paragraph, I combed more of the story together and I think the flow is definitely there at a deeper level.
The goes-without-saying rule about synopsis is that you tell the ending and what happens in between, not leaving much to surprise. But don't take this to the other extreme and share too much. All you'll end up doing with it later is cutting it out because a 500 word contest synopsis can only contain so much information.
Give a nice ending to your synopsis. Something that clearly defines that the story is finished and you know what you're doing, shows that you know how to end a story. The line I choose to end my synopsis with this time was: Conquering failure and fear, With this Dream is a contemporary romance of waiting on God and aligning our dreams perfectly with His.
Sometimes you can take a line such as that and clearly define your genre within the first paragraph of the synopsis, but because my story is very clearly romantic fiction from the first line, I decided to hold this line until the end of the synopsis when I could put it slip it in like a period at the end of a sentence.
I realized something the other day when I wrote my synopsis: writing a synopsis is never easy. I still don't like them, but crafting one does not have to be as hard as I thought it would be. A longer synopsis would be harder, but still holds the same qualities and has room for the same flaws. A synopsis takes R.U.E. to the extreme. So Resist the Urge to Explain and remember: your synopsis isn't about your secondary characters. It's not about how much your heroine loves her dog. It's not about the subplot. It's only about your hero and heroine. So make every word count.