Windex works well as does rubbing alcohol(Easier on you and the rubber than acetone). A little sandpaper does not hurt every now and then (Think of how much grit ends up on a well used MTB rim) but if you use sandpaper wipe it down with alcohol after.
My favorite for dressing pads is a bastard cut file. It will take the pad down smooth in a flash and leaves nothing on the pad. You can get a cheap one for just a couple of bucks.