1 Walls and ceilings
There are countless ways to make repairs to walls and ceilings. Some products are ingenious, like the thin piece of aluminum that has holes in it and self-adhesive on one side. This would work perfectly for filling in a doorknob hole. You simply put the metal patch on the wall and then coat it with premixed drywall compound out of a bucket. The patching compound passes through the small holes and locks the repair material to the metal.
2 Square hole cuts
Another method: Cut a square or rectangular hole using a plunge saw and then remove the jagged drywall. Be sure you look behind and around the hole for any wires, pipes or cables. You don't want to cut these with your saw, causing more problems. Once you have the square hole cut, cut a slightly smaller piece of drywall. Make the repair piece 1 / 4 inch smaller in width and in height. This will give you a manageable gap of just 1 / 8 inch between the repair piece and the existing wallboard. The trick is to fasten this repair piece, as there is rarely a wall stud where the hole was created. Take a piece of wood no thicker than 3 / 4 inch to use for the next step. Cut the piece of wood so it's 1 inch less in width of the hole and 6 inches longer than the height of the hole. Let's say the hole to be repaired is 3 inches square. This means you would cut a piece of wood 2 inches wide by 9 inches long. Plywood works great for this job, as it's not prone to splitting.
3 Gunning it
You'll need a screw gun or a drill with a Phillips bit in it. You'll also need about 10 (1 1 / 4-inch) coarse-thread drywall screws, assuming the drywall is 1 / 2-inch thick. The first thing is to screw one screw into the exact center of the piece of wood so that about 7 / 8 inch of the screw is still sticking out. You'll use this as a finger hold. The trick is to slide the piece of wood into the wall cavity through the hole, making sure you don't drop it in the cavity.
You can tie a string to the screw as a safety device in case you do drop it. Step on the string until you have the wood secured.
Once the wood is in the cavity, center it in the hole, using the screw as your guide. Pull on the screw, so the wood is tight against the back of the drywall at the hole. Use the screw gun or drill to drive drywall screws through the drywall and into the strip of wood as if it were a wall stud. Pull tight against the screw as you do this so the wood pulls tight against the drywall. Use at least two screws, at the top and bottom of the hole, to secure the wood strip. Remove the center screw you were using to hold the wood in place, and then screw the small repair piece to the wood. For a small piece of drywall similar to this example of 3 inches-by-3 inches, you'll only need two screws.
Now, all you have to do is tape and finish the patch. The best way to get proficient at this is to practice on a piece of drywall out in your garage. Once you get the hang of it, move indoors.
The biggest mistakes rookies make when taping and finishing drywall is putting on too much or too little of the joint compound. They also tend to use it straight from the container without adding a slight amount of water to make it creamy like warm cake icing.
7 Making it last
You want about 1 / 16 inch of joint compound under and over the tape to make a lasting repair. If you drag too much mud from under the tape, there will be no compound to bond the tape to the drywall. Too much mud makes a giant hump. The key is to practice taping on a scrap piece of drywall. When the mud is the right consistency, it's easy to draw the taping knife across the tape and pull out the correct amount of mud.