Choosing Your Method
The size of the hole determines the repair method. There's overlap in the ranges, so use your judgment on borderline cases.
Holes 3-6 inches: California patch. Uses the paper facing of the patch drywall as its own backing. Quick and elegant.
Holes 6-12 inches: Backer board method. You install strips of wood or drywall behind the existing wall to give the patch something to screw to.
Holes over 12 inches or multiple holes close together: Stud-to-stud replacement. Cut back to the nearest studs on each side and install a proper piece of drywall.
The methods aren't exclusive. I've done California patches on 8-inch holes and backer boards on 4-inch holes. It depends on the situation, the shape of the hole, and how confident you're feeling that day.
The California Patch
This is my favorite method for medium holes because it's clever. The patch creates its own backing.
The Backer Board Method
For larger holes where the California patch isn't practical, you need to install backing for the patch to screw into.
Stud-to-Stud Replacement
For very large holes or areas with multiple holes, it's easier to cut back to the studs and install a proper piece of drywall.
Use a stud finder to locate the studs on either side of the damage. Mark lines down the center of each stud. Cut along these lines with a drywall saw or utility knife.
Cut the top and bottom of the section between studs. Remove the damaged piece. You now have an opening with stud edges on both sides to screw into.
Cut your patch to fit, leaving about 1/8 inch gap. Screw into both studs, spacing screws about 12 inches. Tape all four seams and mud as usual.
I've done this for holes ranging from a foot square to entire 4x8 sheets. The process is the same, just scaled up. For full sheets, you'll want a helper to hold the drywall while you screw.
What About Wires and Pipes
That first hole I patched had an electrical wire running right through the middle of the wall cavity. This is common, especially in interior walls.
Don't panic. Just work around it. When cutting your patch or installing backing, leave space for the wires. The patch doesn't need to fill every inch of the cavity, it just needs to cover the hole in the wall surface.
What you absolutely don't want to do is nick a wire or pipe while cutting. Cut slowly, look into the cavity with a flashlight before each cut, and if you see anything, cut around it carefully.
My neighbor Maria hit a wire while cutting out a damaged section of drywall. Fortunately the circuit was off since she'd killed power while working. But if it hadn't been, that could have been bad. Always kill power to any circuits that might run through the wall you're cutting into. OSHA safety guidelines stress the importance of de-energizing circuits before any demolition work. Check with a non-contact voltage tester to be sure.
Making Large Patches Invisible
Large patches are harder to hide than small ones because there's more area to blend. A few tips from patches that worked well and patches that didn't:
Feather way out. The edges of your mud should extend 8-12 inches from the patch, maybe more for really large repairs. Thin compound spread over a large area is less visible than thick compound over a small area.
Match the texture. If your walls have orange peel or knockdown texture, a smooth patch will be obvious. Texture the patched area to match before priming. Practice on cardboard first if you've never textured before.
Prime everything. The entire patched area needs primer, not just the compound but the surrounding wall too if you're repainting. This gives you a uniform base for paint.
Paint the whole wall. Touch-ups on large patches rarely blend perfectly. If you want the repair truly invisible, repaint the entire wall from corner to corner.
The closet door punch in my son's room? I did all of the above, and now I can only find the patch if I look closely in raking light. Everyone else just sees a wall.