Anybody have any tips for an upcoming trip to Japan? Such as: stuff you shouldn't do, fight laws (in the unlikely event), drug laws and so forth.

1) Forget drugs.
2) There are beer dispensers everywhere.
3) Try a hot spring.
4) Try and stay in the districts where businessmen fly in to try and get jobs like NE of Ueno and North of Asakusa in Tokyo. Beds there cost £8/$16US a night which is the best you can get in Tokyo beyond staying the night in a capsule hotel.
5) Remember your manners.
6) Visit a shrine.
7) Visit whatever appeals to you.

Like Faithless said, forget drugs.

Excellent; now I don't have to worry about my bungling in an unfamiliar country. Thanks.