writing to potential grad school advisors

[Entwistle, Elizabeth M.]

Hello,
 
I'm looking at potential graduate school advisors right now.  I'd like to write 
letters to them and express my interest in working with them.  I have heard 
that there is a format in terms of content that will help in that endeavour.  I 
was wondering what has helped others in this process or, if you are an advisor, 
what you think should be included in such a letter.
 
Many thanks,
Elizabeth