Many of the students in my class know how to draw well already, but I've noticed that most have a rushed and sketchy approach. Either that or a heavy-handed quality. So I assigned the venerable "Blind Contour" lesson, where you draw slowly and carefully without looking at the paper. I wish I'd thought to photograph these results as they had a wonderful Picasso-esque quality. Then I relented and let them look at the paper for the rest of the afternoon, which in some ways led back to hesitancy, erasure and dissatisfaction. But the point is just to go slow and observe more carefully.
We had Poni modeling for us, a wonderful Hawaiian maiden with natural grace. Of course having a good-looking model can sometimes make a class harder since one then has an anxiety about doing justice to such beauty.