Measure the area around the ceiling damage, and cut a piece of netting that will extend at least 2 feet beyond the damage in all directions.
Place a ladder underneath the ceiling damage, and have someone spot you for safety as you climb up.
Hold one corner of the netting to the ceiling at a distance of at least 2 feet away from the damage. Use a staple gun to attach it to the ceiling.
Repeat the stapling process on each of the remaining corners of the net, moving the ladder as necessary. For larger areas of ceiling damage, apply several staples around the border of the net as well, so it doesn't sag down too far on the sides.