Chuck Miller gives us a great tip for patching a small hole in drywall, such as a hole from an outlet box.
Cut a small piece of scrap drywall about an inch longer than the hole in each direction. Score the back of this piece to reflect the shape of the hole, and peel away the edges. The paper facing that is left on the front of the piece will become the drywall tape because the back of the patch will go into the wall. Apply a layer of joint compound around the hole to hold the patch in place and insert the patch into the wall. Let it dry, then go back over with another layer of joint compound, sand it, apply a third coat, and it's ready to paint.