TRSE How To Draw Tutorials:
Laying Down in 3D.
Step 2 of 5

    The lines can be lightly drawn to help you draw the figure in 3D. Notice how the lines drawn away from their common point (arrow) influences the shape of the figure.  You know how the size of a head is used to determine the length of the entire figure. To make the figure seem 3D, the space nearest to you should be largest (feet seem large) while a space furtherest away from you should be smallest (head seems small). So the length of each space should change over the length of the figure.