Everyone will know how easy it is to accidentally put a hole in drywall; it could be from a door handle, maybe something falling over, or even from children playing. Happily drywall is fairly easy to fix, especially if it is a small hole, It is something that even a novice DIY person can tackle and save paying for a tradesman. If the hole is quite big i.e. anything bigger than 12 inches, it is probably better to replace the whole sheet of drywall rather than making a large patch. Whether the property is rented from a landlord who has good landlord insurance or it is your own property, a hole in the drywall does not mean having to panic.
In the past when there was a hole in drywall, a contractor would arrive, square up the hole and then put in some wooden braces which would support a new square of drywall. However times have moved on and now there are aluminium patches, which will go over the hole without the need to square it up. This aluminium patch is strong enough to fix larger holes, yet it is also thin enough to be covered over with a layer of drywall joint compound. They work in the same way as traditional drywall tape works, where a layer of drywall joint compound is put over the mesh, left to dry, and then 24 hours later a second coat is put on with a larger trowel. The area is then sanded down.
Cracks can quite often occur when the property starts to settle, so it is not that strange to find cracks in a drywall in new and old houses. A crack is very easy to fix by taking a utility knife and make a v-shaped channel along the length of the crack. Fill the crack with some drywall joint compound and then apply some mesh tape over the top (unlike a hole where the aluminium patch works well, it is highly recommended that mesh tape is used for cracks). Once the tape is applied, cover it with some drywall joint compound and feather out the ends. When it has dried, keep feathering it out on the second application and when it has dried, sand it to a smooth finish.
The most common reason for fixing the drywall is filling in old screw holes or nail holes from pictures which have been attached to the wall. Again fixing this is very easy. Take the end of a trowel and tap in the edges of the hole and create a small crater. If the drywall is loose, screw in a new fastener just underneath the hole, then spackle and trowel over the hole, making sure it is filled completely. Wait until it has dried then sand until smooth.