The types of materials you are printing with also make a difference, with the most common consumer options being Acrylonitrile Butadiene Styrene (ABS), a strong but flexible nylon, and Polylactic Acid (PLA) being the most commonly used.
Stuck ABS can be applied using heat or acetone, although acetone should be used last because it can damage the PEI sheet of the printer so it cannot be used. So instead, try heating the print bed to 100 degrees or more to soften the ABS bits, then gently scrape them off with a plastic or silicone scraper.
Caring for nylon is a similar matter, except if you want to glue with heat only (no acetone). Usually a heat gun can do the trick, as long as you can get it to about 375 degrees Fahrenheit (190-degree Celsius). Just hit the nylon with the right temperature to melt it, then carefully remove it from the bed using a plastic or silicone scraper.
PLA is also like doing with ABS, but this time around you have to wait for the print bed to cool down before you start cleaning. Once cooled, use a plastic or silicone scraper to remove any remaining plastic. For stubborn stains, use a clean cloth with a small amount of isopropyl alcohol to wipe the surface of the bed.