As for laws...
While in Japan, remember:
1. Don't shout "Baka Nihonjin" in populated areas.
2. Don't strip and run around naked, with chopsticks in your hair, yelling "Kuru-kuru-pa".
3. Don't ask to see a Yakuza's tattoo and little finger.
Okay, for the real ones that you might not know about:
A. Don't make too much noise.
B. Don't blow your nose in public - go to a restroom first, it's considered rude, although some people are doing it more often now.
C. Bow a little bit.
D. It'll be good if you have learnt some Japanese, and be polite.
E. Don't worry if people move away from you when you sit down on the train.
F. During rush hour on the trains, expect people to elbow you out of the way - it's acceptable and expected...If you want to do it, politely push through people, with an audible, "Gomen, Gomen"