Overlap
 This is the most basic way to indicate distance to the viewer--one object overlaps another.





 

Linear Perspective
Linear perspective helps us give any object proper size and placement, as well as keep all our shapes and receding lines in correct proportion to each other.   The general rule here is that parallel lines that recede will always appear to meet at a vanishing point somewhere on the horizon (eye level of the viewer).   For one example, you can see the road edges moving closer together as they recede.  The vanishing point shifts when the road changes direction.

Color
 The earth's atmosphere fuzzes up how we see things over distance.   For this reason, distant objects appear differently to us than nearby objects.  For this reason, we have the concepts of aerial perspective.  Warm colors tend to move closer, and cool colors tend to recede.  Also bright colors tend to be in the foreground, and dull down as they recede.   If you look at the flowers  in this example, you can see that they get duller as they recede.

Detail
 Following the concepts of aerial perspective, there is usually more detail in the foreground and less in the background.  In this example, note more detail on the foreground shed when compared to the shed in the distance.




 

Edge
In aerial perspective, edges in the foreground are sharper, edges in the distance are fuzzier.  Here, you see sharper edges of the shed compared to the fuzzy edge of the hill behind it.

Value
 In aerial perspective, dark values tend to move forward, and light values recede.  Here, you can see a shift in values between the closer ridge and the farther ridge.