Step 1 - Draw a repeating square until it shrinks into tiny dots.
Step 2 - Change the direction of the squares.
Step 3 - Start with those tiny dots and grow the squares.
Step 4 - Draw another set of shrinking squares to go behind the first set to show overlapping shapes (front/behind).
Step 5 - Shading was introduced.
Step 6 - 18 inch rulers where used to draw vanishing lines in the background. (Some students had a hard time keeping the ruler from slipping as they drew.)