One exercise that I remember from school (though I can't place it to a particular year) involved writing instructions which another student would then follow to reconstruct a drawing.

The goal was to get the reader to draw out each letter of a message, but you weren't allowed to use the names of letters, and the reader didn't know the instructions were meant to make a message. So the instruction "draw a half-circle pointing left, with a line connecting its ends" might get you the capital letter D, or it might get you this.

Now that I think about it, this may have actually been in an art class, not even a writing class, and the point of it may have been to get people thinking about shapes, not instructions. But I may be confabulating that.