When the meal is over, don't leave your napkin so that the side you patted your nose with is on the outside. Don't ball it up and throw in on the plate. Don't fold it up as if you're folding a pillow case, just leave it neatly on the table. Feel better!
Just an aside - after a dinner party at a friend's home in Milan, Italy, I folded my dinner napkin up as if it were clean laundry. The host said, "Never do that. I it means you're never coming back to my house."