Cut a small hole around the nail bump with a utility knife. Scrape out the section of drywall in the center of the hole.
Use a nail set and a hammer to tap the nail into the drywall slightly, making sure it is well set. If it doesn't seem to be grabbing well pull it and replace it with a new nail or a drywall screw.
Cut any excess paper from the face of the drywall out of the hole to make the edge clean and defined.
Apply a small amount of drywall patch to the hole with a putty knife and spread it flat. Be sure to fill the hole completely by pressing the patch in with the knife.
Scrape any excess off the surface with the knife and allow the patch material to dry.
Sand the patch smooth. If the wall is smooth this area is now ready for paint. If the wall is textured, use canned spray texture in short, consistent passes to over the new area with texture. This may take several applications. If the texture becomes too thick in this area it can be sanded off and reapplied.