Commander Mark's Secret City
Foreshortening: Take a circle or a square and turn it on it's side.
Shading: You put shading on one side on an object, it helps it look 3 dimensional.
Surface: You have two objects. If you draw one object lower on the piece of paper, it looks closer to you.
Size: You draw one object LARGER than the other, the larger one looks closer.
Overlapping: Draw two objects and make one of them overlap the other, it will look closer.
Contour: If you draw a cylinder shape and draw lines wrapping around the contour of the shape, it looks more 3 dimensional.
Density: If you have two objects and you draw one object really faint and hazy in the back, the other looks closer to you.