I would take a trip to the book store and look through a book called The Artist Market. I has tons of information on the business market place for artists, which illustrators fall into. You probably want to make sure you understand Copyright as well. Make it clear to your client as whether or not you're releasing the copyright to your illustrations indefinitely or for a specific print run etc. I'm sure Gary Priester, he's more involved in the Xara Xtreme group, can speak to this as he's located in a area of the world known for artists and such. Speaking from experience, artists need to watch their backs sometimes.

Good Luck,