Mask off windows, walls or any other items that you do not want to get the texture compound on, using newspapers and masking tape. Do not mask walls if they will be painted later.
Mix the dry ingredients of the texture compound with water according to the directions on the bag. Let the mixture set up for the proper amount of time advised in the directions before you begin. Skip this step if you are using a premixed compound.
Pour the compound mixture into the plastic hopper of a texture sprayer. Set the pressure on the sprayer according to the directions that came with the machine. Plug the sprayer into a wall outlet and turn it on.
Hold the sprayer 12 to 18 inches away from the ceiling and depress the trigger on the handle. Move the sprayer in long, sweeping motions to apply compound evenly across the ceiling. Continue until the entire ceiling has an even coat of the texture compound.
Flatten out the joint compound applied to the ceiling using a knockdown tool, which is available at drywall supply stores. Drag the rubber edge of the tool across the ceiling evenly from one end to the other. Repeat until the entire ceiling has been covered with the tool.
Scrape any splattered compound from the walls --- if you did not mask earlier --- with a 12-inch flat drywall knife while the compound is still wet. Use a smaller 6-inch knife with a sharp edge to get close to the ceiling.
Allow the compound to cure for the time specified in the directions on the compound container. Paint the ceiling, if desired.