3M 220-Grit Sandpaper
This is the exact sandpaper I use when sanding my parts – including after applying spackle. If your part is extremely rough and needs tougher sanding – you will want to go with a lower number (80 -150 grit), but really you shouldn’t go with a lower number than 220 for most practical puporses.
If the part you are working on is very sensitive and needs fine sanding – you can work your way up to 2000 grit for the smoothest print possible. That said – this is the main sandpaper I use.