location, conflict, characters as necessary
Within the provided framework of the location and conflict, the actors must build a scene with an important twist: at all times, one actor must be sitting, one must be standing, and one must be lying down. If one changes positions, the others must change as well, but the key is that there must be motivation behind each move. For example, at a campsite, one actor might be sitting by the fire, one standing near the tent, and one laying down on a bedroll. The sitter might stand and say "Wow, would you look at the stars," the stander might pretend to be bitten by a snake and fall to the ground so that the layer will sit to tend to the snake bite.
Provide locations and conflicts that lend themselves to movement. Three characters in a church service might be a comedic challenge, but if it doesn't generate laughs, it's dead. Try to pick suggestions such as working on a car, inspecting a factory, building a scaffold, etc., wherein the actors must move as a result of the scene. This will be much more natural and funnier as the actors can concentrate more on improving than trying to come up with reasons to move.
One fine day in Canada, a chair gets fixed, pancakes are served, and a man meets his untimely demise.