Certain sandpapers work better than others, I use Norton Dry Wall sandpaper for all my glass calls, it holds up much better then regular sandpaper does and it cuts the glass a lot easier. It's a silicon carbide sandpaper that works dry or wet. Primo's slick stix wroks very well on glass calls but they do ware out if you have a lot to do. The carbide screens work good and so do diamond sharpening stones, but the sandpaper is the cheapest and works just as well.
There are a few companies that produce soundboard stickers but you limited to certain sizes, A lot of guys print a pic, glue it on then cut it to size as SpitnDrum said above.