The lessons must be high-level enough so students can understand them, but concrete enough so they can be solidly mapped to examples in the real world. The students must hide their drawings from each other. At the top of the page, draw a blue triangle. Draw a purple circle below the blue triangle. Draw a blue rectangle below the purple circle.
Students then trade instruction sheets, and follow the directions on someone else's.
They don't know what they're supposed to draw - they have only a set of instructions to work with. Finally, the students compare their original drawings with what the person who followed their directions drew. The next step is to discuss what went wrong and how to fix it.