Patching a hole in drywall is not a difficult job, but it is a bit time consuming since you must allow for each phase of the job to dry completely before starting the next one.
If the repair work that needs done is hairline or a small dent, you can easily repair it by applying several coats of joint compound, allowing it to dry, sanding it and then priming and covering it with existing wall covering, such as paint.
If the repair needed is larger than a small crack or dent, more extensive measures will need to be taken to do the work and you can follow these steps:
First of all, know that working with a hole that is irregular is difficult when using drywall, so you want to cut the hole, using a saw especially designed for drywall, into a shape that is easy to work with for patchwork, such as a rectangle or square. Make sure to wear safety goggles and a dust mask , or even better, a respirator, on your face because drywall work leaves many particles in the air that you do not want to breathe in. Drywall work is messy work.
Now you want to cut a piece of drywall out of material that is the same as the existing drywall (for example, if you are repairing drywall that is green board or waterproof, make sure the drywall you are using for the repair work is of the same material).
Attach the newly cut repair patch to the existing hole by screwing it into an exposed stud within the hole. If a stud is not visible you simply need to screw (with drywall screws) a piece of lumber from one side of the hole to the other. Measure and cut an appropriately sized piece of wood to get the job done, making sure to countersink the screws as you go. The piece of wood serves as a support piece for your patchwork. All work should be done with countersunk drywall screws.
Use fiberglass mesh tape to cover all four seams where the new piece of drywall has been placed.
Evenly spread joint compound to completely cover the tape. Feather the edges to be as smooth as you can get it.
Allow to dry completely and then sand it smooth with sandpaper. Do not use a power sander.
Apply another layer of joint compound and allow to dry.
Sand with a fine grain sandpaper, by hand.
Apply primer to the spot and allow to dry.
You are now ready to paint or put in the patch wallpaper to finish up the job.
The important thing to remember here is to allow room in between steps for the work being done to dry completely. If you rush the job and do not allow it proper time to set, it will crumble, dent, or be too weak to be considered a proper repair job. It is not a hard job to do, but it takes patience. If you take time out to do the job well, it will prove to be worth the effort in both strength and in appearance.