Mineral spirits.....should be able to get it from your local hardware or maybe automotive store. It's fantastic stuff, I used it to remove the dealer stickers on my bike and my car a few months back. Get all of the messy glue stuff off and doesn't hurt the paint at all.
I pull gently and back on itself as much as possible (bad description but same idea as painting tape or a band-aid). Then I dab at any remaining residue with the sticker itself. Usually that's enough to get everything but if not I'm also a goo gone user to clean up the rest. Incidentally I usually find it easier on a warm day.
I worked at a computer refurbisher a few years back and for sticker removal the best thing we had was called Un-Du.
You can get it on ebay if nowhere else. The bottle should have its own plastic scraper as shown, otherwise a credit card should work. It's never damaged any paint or plastic I've used it on. If it's a plastic sticker, you have to keep dripping some on the edge as you pull the sticker up, and keep using drops of it untill all the glue scrapes off. I run a paper towel over it and once it doesn;t stick, all the glue is gone!
Good god stay away from using razor blades!! Yikes!!
Heat gun or hair dyer and a credit card gets most of it off. Then use mineral spirits (paint thinner), WD40 or Goo Gone to clean off the remaining residue.