Sanding your interior walls can be a messy job and most homeowners I talk to don't like dealing with all the dust. If your walls are in good shape you won't need to sand ahead of time. If you do have to sand 80-100 grit sandpaper on a sanding pole is what I usually recommend. This will remove the imperfections from your wall.
Quick Episode Summary:
0:17 Is Sanding Necessary
0:49 Sanding Your Walls
1:12 Sanding Your Trimwork
1:39 Sanding Your Ceiling
1:58 Quick Tip