How to Make it Look 3D

Okay - here are a few tricks to put up your sleeve:

Overlapping & Shadows- set up a group of objects that are close together and overlap each other. Pick out where the light will be coming from and then put in some shadows. See the Cezanne example below.

Atmosperic Perspective - as objects get farther away try this: their colors become pale/less strong and start to resemble to background color (bluish mountains against the sky, reddish mountains during the sunset). There is also less of a dark/light contrast between the fartherest away objects and the background. Finally - closer items will have definite details. Farther items have less detail. There's a photo of mountians below.

Vanishing Point - parallel lines get closer together to form a V way out in the distance/horizon. This can be the lines of a street, railroad tracks, any object that is both close and far. Check out the photo below of railroad tracks.

Perspective - make far away objects smaller than like objects that are close.