Soak the glass with warm, soapy water
Let it sit for a few minutes
Scrape gently with a plastic scraper or old credit card
Apply rubbing alcohol to a cloth and rub the glue
Use white vinegar on a cloth for stubborn residue
Apply a small amount of cooking oil or baby oil
Wipe away the softened glue
Clean the glass with glass cleaner
Dry with a lint-free cloth