if they're nude photos, find out what rights you will have with them. Does he want all the rights to the photos, meaning you can't use them for your portfolio or repost them anywhere? Be sure to get this out of the way up front, you may even want to look into drafting something in writing in case it gets ugly.
Here's some quick info:
http://nudemodelssite.com/info.php
Look on the net for examples of contracts and such.
Also, bringing a friend wouldn't be a bad idea, especially for you first time working with the photographer. If he objects, he's not worth your time.