When teaching my elementary students how to create landscapes, recently, I emphasized three vocabulary words: foreground (what is closest to you), background (what is farthest away from you) and middle ground (what is between the foreground and the background). I started with three objects, a stapler, bottle of glue, and roll of tape. I asked which object was closest, which was farthest, and which was in the middle. Because my students are legally blind, they needed to figure out what the objects were and where they were located by touch. We touched each object and said, "closest, farthest, and the middle" than we continued touching saying "foreground, middle ground and background." I repeated asking, "What is in the foreground?" They'd answer, "the stapler." or "Where is the glue?" They'd answer, "in the middle ground." It took a lot of practice, but once they understood the concepts reaching back on a table, I brought out the art history posters like this one of a painting by Thomas Cole.
These images, I would describe in detail, and they would sweep their hand across the foreground, (usually at the bottom of the poster), the middle ground (usually in the middle of the poster), and the background (usually at the top of the poster). For older students I use the terms like "vertical placement" and "overlapping," when I talk about ways to show depth on a 2D surface.
Once they grasped that idea, we made very simple images with colored pencil and tissue paper with foreground at the bottom, middle ground in the middle, and background at the top.
The following week we started over with the same exercises, but this time, they choose a color of paper as their background. They painted branches for the middle ground, and then they each put cherry blossoms in the foreground, using either a sponge, a celery heart, or soda bottle to stamp blossoms. Our town is spectacular with its 10,000 cherry blossoms in bloom, so it's nice to celebrate while reinforcing landscape vocabulary.