I was looking at writing books on Amazon, and found a really killer "inside peek" of a book on screenwriting that totally nails how to do a one-liner description. It's called Save The Cat: The Last Book on Screenwriting You'll Ever Need by Blake Snyder.
What he says is to think of how you would pitch your story in one sentence to friends who are looking in the newspaper for a movie to see on Friday night. This is called a "logline." For example:
A businessman falls in love with the hooker he hires to be his date for the weekend. - Pretty Woman
A cop comes to LA to visit his estranged wife and her office building is taken over by terrorists - Die Hard.
He also says how important irony is - all these situations are ironic in some way.
So after reading this I thought,
Well, heck then, my logline is:
A Ranger has to rescue the girl he's secretly in love with, after she puts herself in danger to protect him.
(insert gratuitous photo of Hugh Jackman here -----> )