There are a few common methods to doing this.
Dilute some rubbing alcohol with purified water, then use a Q-Tip and apply the solution to the sticker. Do not get the sticker too wet, because excess water will damage the card. If done slowly and in moderation, the mixture will loosen the sticker, and it can be gently pealed off slowly using your finger nail.
A product called UNDO seems to be popular, and it comes with a scraper built on to the bottle lip. Once again, use it moderately, and scrape the sticker off slowly. Also, wipe up any excess quickly.
Other products that have been shown successful are GooGone and lighter fluid, using the techniques above.