• linear perspective
• aerial perspective
• contrast of values
One that I use most often is the angle and plane concept.
The change of value on a flat horizontal plane is different than that on an inclined plane. To make a plane in your painting appear to be horizontal, the amount of change of value needs to be within a 10 percent range. More of a change will make the plane inclined.
Adding more contrast and details in the foreground helps create the illusion of depth.