Most points already covered, but here are a couple of minor additions. Clean your ears out and dry them thoroughly. Cut your nails short. Clean between your toes, a small air line type tooth brush is useful just for that. If you use cologne or aftershave do not put any on anything you hope will be kissed or sucked - it tastes horrible. Remember that Japanese and Koreans tend to prefer very subtle fragrances so don't overdo it. And if the shop has a shower before service requirement, never bitch about an additional shower.