The University of Michigan Law School has one of the best waitlist FAQs I have ever seen . Kudos to Michigan Law School. If you are waitlisted, read this page thoroughly.
"Indicating continuing interest and availability is a good way to stand out when you're on a waitlist. If you receive any new honors, awards, or grades, or get a new job or a promotion or take on a volunteer position, you should definitely let us know. If you would like to have an additional letter of recommendation submitted, that can be helpful as well. If nothing in your life has changed, but you want to indicate your ongoing interest, that alone can be helpful; feel free to send us a letter or e-mail. Again, because of the time constraints inherent in a waitlist, the last thing we want is to make a call to someone who is no longer interested in being called."