Either picking up a small container of Spackle or Painter's Putty at your local hardware/home improvement store. I grabbed a small container at ACE the other day for less than $5. Quick, easy, no fuss no muss. Just use either to fill in/over the whole. Allow to dry and then smooth out with either a very fine grain of sandpaper or a sanding sponge. Then you are ready paint over it if need be.