I took life-drawing classes in college. A lot of good advice has already been shared - re: the difficulty to hold a pose and that it's cold. Bring a robe or something you can easily put on/off during breaks.
As an artist, I could really have cared less what the model looked like. Though occasionally we had one model that was incredibly thin, and it felt like drawing a sick figure. The artists are drawing the shapes, not really paying attention to the person.
And I agree that the best models were the theatrical ones - poses actually doing realistic motions like reaching for something, picking something up off the ground, sometimes models used props like tennis rackets or swords - incredibly helpful.
Working with a good model is an incredibly valuable experience for an artist. Life drawing one of the most fundamental skills, and there's a lot of preparation and planning that go into being a good model. Think about the types of poses that would be beneficial to the class. Is it a traditional figure drawing class, or are the students in a particular training program? For some groups, action poses may be more in demand, and another may need more classic poses. Video game or animation students would have completely different needs from MFA students.
I got a laugh out of this :)
Having been on both sides of the easel, my advice is if anyone is a jerk to you, you can get back at them in a passive aggressive way by posing with an arm or leg outstretched in their direction. Foreshortening is a pain for beginning artists to draw well.