A quick example of an elevator pitch

"What if a serial killer videotaped his own murders and then sent that video to the cops?"

That's the first line I give for my novel Beholder's Eye.  There's more to it, but essentially, when I first thought of this book, that's the what if question I came up with.

Now, this isn't the entire elevator pitch, but this gets me started.  Try yours out on a group of people.  If you are part of a writers' group, pitch them and see what they think.