What do you clean it with? There are special cleaning solution for it, and you shouldn't use anything abrasive to scrub it with. For any spills, plastic included (ask me how I know), you use a glass top scraper to scrape it off. (just make sure to use it under a sharp angle and change the razors when damaged) You should also raise pot/pans when shaking them instead of sliding them on the glass.
If the damage is already done, you can just use a polishing compound and remove most of the scratches.
Miele has a cool design on its induction tops where there are little raised white bumps in the cooking zones, these prevent scratches from pots and pans. (They also offer a "diamond" finish, but I don't know how good that is)