Herewith, the Seven Magic Words:
*Foreshortening. This creates the illusion that part of an object is closer to you than it actually is. The near corner of a drawn cube, for example, appears to be nearer merely because it is drawn lower. The top of the cube looks like a diamond, but it's actually a foreshortened square.
*Size. Quite simply, the larger you draw an object, the closer it appears.
*Surface. The lower you draw on the surface of your piece of paper, again, the closer the object will look to you.
*Contour. This helps create the illusion of a three-dimensional drawing, by drawing textural lines around cylindrical objects such as sleeves, to give volume and shape.
*Overlapping. If you draw two mountains side by side, the illusion of putting one line over the other will make one mountain appear to be closer than the other.
*Density. By drawing more detail in the foreground and less in the background, you will help create the illusion of depth.
*Shading. By shading part of an object and creating shadow areas, you lead the eye to make judgments about which part of the object is in front, in regard to its relationship to the light. Again, it creates a sense of depth.