Place the tip of a nail set or awl in the hole. Tap the end of the nail set or awl just enough to indent the hole. Nails usually leave a raised edge when removing them from the wall. The awl or nail set compresses the raised edge back toward the wall.
Fill the hole with general-purpose compound using the corner of a putty knife. If the hole is small, such as a brad nail hole, squeeze the compound into the hole with the corner of the putty knife blade. Scrape off any excess compound so it is flush with the surface.
Allow the compound to dry thoroughly, if filling a larger nail hole. Sand the compound even with the wall surface with 100-grit sandpaper. Wipe the patch area clean with a damp cloth.
Apply another coat of compound over the hole in a crisscross pattern. Allow the second coat of compound to dry thoroughly, and sand it flush to the wall surface with the sandpaper. Wipe the nail hole patch clean with a damp rag. Paint to match the rest of the wall.