Drywall is fragile, especially when it is being repaired. If you need to use a hammer, use a drywall hammer with a rounded tip to prevent the paper from ripping (or from ripping further). You will probably need to use some type of putty knife or paint scraper in your work, but try to find one without sharp edges to avoid creating further damage.
If your drywall paper has ripped but can be repaired, use drywall paper tape, which is designed to seal tears in your drywall. If you have difficult corners or seams that need to be repaired, use self adhesive mesh versions instead of normal drywall tape.
If your drywall paper is exposed but not torn, you can cover it up with spackle and apply a layer of joint compound to blend the area in with the surrounding drywall. You may need to sand the area down before adding the last layer. If your drywall paper has ripped, use your drywall tape, and then cover it up with three layers of joint compound to ensure that it is fully blended in.
Always seal your drywall when you are making any repairs, which helps to protect the drywall against damaging moisture that can creep in through air and paint afterwards. Brush the drywall with either a sealer designed for drywall or a primer that has sealant capabilities.