He teaches them good manners and social mores, and he expects them to be just as well-behaved in private as they are in public.
In other countries, there may be variations based on the cultural mores, such as head scarves in Muslim countries.
He also has encyclopedic informations on cultural mores across the galaxy - just the droid you would want at your side to keep you from committing the odd destruction-of-your-race faux pas when dealing with aliens.
Mork was an ET who was taken in by human Mindy, and humor was found in his inability to understand human cultural mores and norms.
So in effect, writing science fiction is harder than writing 'plain' fiction, since you have to know how to write fiction AND how to world-build and all the conventions and mores of the science fiction genre.