I've always found that WD-40 is a great way to remove sticker residue that gets left behind when you remove a sticker. Just spray the residue with WD-40, let it sit for a minute, then rub with a clean cloth to remove the residue. I've never had the WD-40 stain or remove paint when doing this, but it's always a good idea to test on an inconspicuous area first to make sure the WD-40 won't harm the surface.