Scrape away loose debris, apply lightweight spackling over the hole and let it dry. Add more spackling if the hole isn't filled. Then sand smooth. For pop nail heads, drive into the drywall and screw about one and a half inches above or below to hold the drywall. Then drive in the pop nail, spackle and sand. Holes from a door knob can be fixed with a small patch kit. Stick the patch over the hole. Then use a drywall knife to cover with spackling and a curse