Sketch a rough drawing of a backdrop you'd like to use for a particular scene. This does not have to be detailed or beautiful. Rather, it should indicate the basic layout of the background. For example, if you're shooting a that's supposed to take place near a mountain, your sketch will indicate the rough outline of a mountain in the background.
Determine the necessary dimensions of your backdrop. If your scene contains a lot of movement, such as actors walking from side to side or toward the backdrop, you'll need a large backdrop. If your scene happens in a smaller space without significant movement, the backdrop can be small.
Paint the backdrop. If the backdrop is very large, you'll probably need to use cloth as a canvas. Smaller backdrops can be made with poster board.
Film a test run of your scene. After reviewing the footage, you might decide that you want to make some change or additions to your backdrop, either to increase its realism or reduce its visual priority within the scene.