I spent the first 10 minutes of each class, just like you, assigning seats and going over the art room rules. My number one rule is YOU CAN NEVER MAKE A MISTAKE IN ART!!!
I went over new classroom incentives, like artist of the week, which I stole right off of Art Room 104. This is for my 3rd, 4th and 5th grades only. Children who remember all of their supplies, put in effort, help their friends, and maintain a positive attitude can be artist of the week which merits a one time pass to switch your seat in class.
I pointed out areas where only Mrs. Miller is allowed to go, like my roving paint station:
That's about it!