Dents
Simply sand over the dent and fill with joint compound. Add a second coat if necessary. Sand and prime when dry.

Holes and Cracks
Wipe the area clean and fill with joint compound. Add a second coat if necessary. Sand and prime when dry.  Popped Nails Drive and dimple a new nail 1-1/2" from the popped nail. Drive and dimple the popped nail. Cover with joint compound, then sand and prime when dry

Medium Size Holes
Apply generous amounts of joint compound around the edges and coat the perimeter of the hole. Crisscross two or three strips of joint tape over the opening and embed the tape in joint compound. Let harden. Apply a coat of joint compound over the taped area. Let harden and apply a second coat. Sand and prime when dry. Large Cracks (1/8" or larger) Apply compound to crack with a 5" finishing knife. Embed tape in compound to bridge crack. Draw knife firmly over crack to tightly embed tape. Let compound harden Apply compound over tape with knife. Let harden and apply second coat of compound if necessary. Sand and prime when dry. Torn Gypsum Panel Face Paper Peel and remove all loose face paper. Apply a skim coat of joint compound with a joint finishing knife over the damaged area and feather to get a smooth finish. Let dry and apply a second coat, if necessary. Sand and prime when dry.

Large Holes
Lets says the door slammed into the wall and the knob went thru the wall.  Cut a piece of drywall appx 8" square,no need to get a square and all that,just eyeball it.  Now take the pc you cut,layit over the hole wirh the hole at appx center,trace the outline of your cut piece onto the wall.  Using either your razor knife of a small saw,cut arout the lines and cleanout the hole.  Your cut piece should fit in nicely.  Now take 1 small pcs of  1"x 2" at least 12" long,  and stick it in the hole,center it left to right and attach it with a drywall screw thru the drywall into the wood making sure the screwhead is slightly below the surface of the drywall face.  One on each side should do.  Larger holes will require two or more pieces.  Now simply apply some joint compound to the backside of the repair piece (buttering) set it firmly into the hole and gently push until it is flush.  Finish off per instructions for medium holes applying tape to the four outer edges.

Have a small repair to do?
Take a look at our Complete Drywall Repair Kit