I haven't had occasion to clean mine, but I would probably start by popping the screen out and trying warm soapy water. I'm not sure I would try to do any wiping or scrubbing though, at least not on the "ground" side. If there's grease pencil type stuff, lighter fluid (naptha/mineral spirits) could probably be useful and is fairly benign as solvents go but usually effective on adhesive goo, marker pen ink and waxy/greasy stuff. "Wash, rinse and blow dry." Handle the screen by the edges, I believe the surface is pretty delicate.