Glass can be scratched and damaged by many different surfaces, like fingernails and other pieces of glass. Even loose dust in the air can land on the glass in your camera lens or on your cell phone face and scratch the surface.
You can rub out tiny scratches on your glassware by using a dab of toothpaste. First, wipe down the glass with a cloth, so the surface is clean. Then, completely coat the scratch with the toothpaste and gently scrape off the excess. Let the toothpaste dry before wiping it off with a cloth.