Right off the top...
When offering something to someone else (your business card, credit card, money, etc.), hold it with both hands. Similarly, accept things offered to you in this manner with both hands.
If you receive a business card from someone, don't just stuff it in your pocket, especially your back pocket. It's considered insulting.
If you bow, don't just incline your head, even if you aren't going to bow very far, bend from the waist.
Take a bath before jumping into a o-furo or hot spring, and don't wear a swim suit when you do.
Don't wear the 'WC' slippers outside the restroom. Yuck. Only Izumi Curtis can get away with this sort of thing.
Slurping your noodles (if they are served in broth) is okay.
Learn the phrase "onegai shimasu"; it's polite and greatly appreciated when we used it. That and "sumimasen" were very very useful.
That's all I can think of for right now...
Hope that helps a little...
