I by no means know how to work leather very well, but what I did seems to have worked for me: I started dry-sanding at about 400 grit, moved up to 600, 800, 1000, 1500, and then 2000 until I had a nice smooth surface. It definitely has to be dry sanding. It really didn't take very long at all, and I don't feel that I really took that much material off.