1.   Add succeeding layers until the hole is almost closed, then fill in with compound, smooth off, let set and sand smooth.

2.   After this dries, sand smooth with fine paper before the first coat of varnish is applied.

3.   Do this with medium sandpaper or a plane, then sand smooth.

4.   If that happens, the only thing to do is fill them with joint compound and sand smooth.

5.   Scrape off excess and wipe smooth with a wet sponge, or wait a few days and sand smooth.

6.   Smooth off, sand smooth, and repaint.

7.   When you are ready to take it down, just fill the holes with joint compound, sand smooth, and repaint.