Tell them WHY they are your 1st pick. You could say something like "Dear Mr. Law School Dean,During the months following the submission of my application, I have been doing additional research on the law schools to which I applied. The purpose of this letter is to share with you the reasons why I have come to the conclusion that the University of --- is my number one choice law school and why I would be an exceptional addition to the University’s student body."If you need ideas on programs, go to their website. Be careful promising attendance though, unless you are absolutely sure you mean it.