Using descriptive vocabulary have the students draw something that you describe, or better yet, that another student describes. I had students each draw a person, they were encouraged to make the person wacky, and then I had students go to the board and listen to their classmates. They drew what they heard without looking at the other student's drawing. The class voted on which drawing they liked best.
This could work with anything, animals, houses, classrooms. Example- "The classroom has three windows and 10 desks. The teacher looks like a giraffe. These are 2 students. etc."
Everyone had fun with the descriptive lesson and it was really funny to see the students' quick artwork.
