According to SFGate, there are many steps involved in the process of spraying drywall textures. The orange peel method provides a lighter texture and the popcorn method provides for heavier coverage.
Before spraying, remove furniture from the room. Mask any wall edges and trim using painter's tape. Place plastic sheeting on the wall and ceiling in order to protect them from being sprayed. Next, clean the wall with soap and water. Rinse the wall and give it time to dry. Use a putty knife to apply three coats of drywall compound. Allow the compound to dry between coats. Sand the final coating with 100-grit sandpaper, then prime and paint the wall the same color as the desired texture.
Next, mix the plain drywall texture with either water or paint inside a bucket until it has the a pancake batter consistency. For the lighter texture of the orange peel method, use a drill with an attached paddle to mix the texture. For the heavier coverage of popcorn texture, let the drywall texture sit in water or paint according to the package's directions, then let it sit for 3 hours before using the drill with mixer attachment.
Next, fill the hopper with the mixture and attach a narrow nozzle for orange texture or a wider nozzle for popcorn texture. Connect the hopper to an air compressor and set the compressor to 30 pounds of pressure. An optional step is to tape large sheets of paper on the wall to practice spraying in even strokes. When ready, spray the actual wall and use the flat edge of a trowel to even or flatten the texture as needed.