Pictorial Depth Cues
Parallel lines are made to converge as they extend.
When objects overlap, the overlapped object appears further away.
The closer the object is, the more detail it has. The further away it is, the less detail it has.
If the object is bigger it is closer, and if it is smaller it is further away.
Height in the Visual Field
The closer something is to the horizon, the further away it is.