Focusing on positive vs. negative shapes. Shapes inside shapes are throwing lots of students for a loop. "Do I flip this Mr. Mintert?" was said quite alot. Two sizes of colored paper, one half size, the other is the base. Draw a design on the small sheet, cut out shapes and glue them down. Usually easier if you glue one piece at a time, and use the leftover piece as a guide to figure out where parts get laid down.
Here are some of the wonderful resuts. Owls were very popular.
This lesson was modified from the original posted by Blick here.