Everyone probably has their favorite technique, so I'll bet you get lots of answers.
I start with a hair dryer on medium heat. Oftentimes the heat loosens the glue underneath the sticker so that you can carefully peel it off.
I've had a lot of luck with wallpaper paste remover. You can get it at any paint store. I just saturate a cotton ball with it and carefully rub until the sticker is gone. So far I have never damaged a dust jacket doing that and been able to remove most all of the stickers I have tried it on.