Overlay objects that you want to appear closer so that they partially cover objects that you want to appear farther away. Make the objects in front (foreground) larger than the objects in the distance (background).
Draw the objects in the foreground at a position lower on the paper than objects in the background if the objects are below your eye level. Draw the objects in the foreground at a position higher on the paper than objects in the background if the objects are above your eye level.
Don't shade things you want to appear in the foreground or shade them with light shades of gray. Shade things you want to appear in the background with dark shades of grey or black.
Develop the composition such that there is a stark contrast (difference in darkness of shading) between things in the foreground and things in the background. Don't create 3D compositions with things that are all shaded at the same value of light or dark.
Develop the contrast such that it emphasizes objects that are closer with larger sizes and wider lines. Use curvature and angles of lines to emphasize the fact that curves and lines on an object recede to a common point in the distance.
Draw things that are to appear in the foreground with sharp, crisp lines. Draw things that are to appear in the background with fuzzy or poorly defined lines.
Shade objects that you want to appear closer with higher levels of contrast. Shade objects that you want to appear farther away with lower levels of constrast.