i use a cleaning cloth that came free with my glasses. It's made of some material called microfiber i think and i have seen it for sale for cleaning camera lenses too. I wet the cloth thoroughly and then very carefully wipe the screen, rinsing the cloth often in between to make sure there is no sand or other abraisive stuff around that could cause scratches. I have done this every few days for over two years and the screen doesn't have a single scratch.