Japan has been quite isolated for many centuries in the past and hence developed a unique culture and very specific rules of conduct. Social status for instance, plays a very big role in the Japanese society. All the rules are quite difficult to understand for foreigners and there's quite frankly a lot you can do wrong here.
However, on basically every visit to Japan I've noticed that the Japanese tend to be very (like extreeeeemely) indulgent and helpful to foreigners and many of them generally have like no expectations for you to behave anything like a Japanese person would.
Anyways, if you're interested in Japan and are ever planning to visit the "country of the sun's origin", here's some things you should or shouldn't do:
1. Shoes, shoes, shoes
Don't leave your shoes on when entering someone else's house!
This is considered impolite and very bad manners in Japan.
2. Be modest
If someone gives you a compliment, don't just say "Thank you.". If they for instance tell you you have beautiful eyes, say something like "Oh, they are such a boring color though." – seems weird and impolite to us westerners but is the only correct reaction to flatteries in Japan.
3. Greetings!
Greet people with a mild handshake or a slight bow, avoid excessive eye contact.
4. Can't touch this!
Don't get too close to strangers, like.. Physically. Physical contact with strangers is usually avoided.
5. 日本語
Learn Japanese before you go to Japan. While most people will probably use English when talking to you anyway - your stay in Japan will be much more pleasant and easygoing if you know at least some basic Japanese!
6. Business
Don't underestimate the importance of cards if you're in Japan for business - always give and receive a business card with BOTH hands.
7. Control your temper
Don't criticise people or show negative emotions openly in Japan. This is very important if you don't wanna be considered impolite. If you disagree with someone's opinion or ways in general always tell them in the politest possible way.
8. Finger food!
Do not eat sushi with chopsticks in Japan - not even if you're very proud of your skills with chopsticks. Sushi is finger food in Japan, so don't be a weirdo.
9. Generosity
Be generous - the Japanese love receiving and giving small presents as an expression of mutual appreciation every here and then, if you receive a gift from someone it's only polite to get them something in return.
10. The snot...
Don't blow your nose when you're out in public in Japan, that is something seen as very nasty and inconsiderate here. If you're out in public and feel like something's coming, pull it up!
11. Slurp that soup!
The Japanese cuisine offers an incredibly tasty variety of soups and noodle dishes. Slurping is a sign of relish, so don't be hesitant to eat your soup noisily. Don't burp though - that's just as impolite in Japan as in pretty much all other places..
12. Don't give tips!
You generally don't give tips in Japan, in fact, that can even be seen as offensive as a good service is a 'matter of honour' in Japan.
13. Don't jump the queue!
The Japanese are the champions of queuing..
Hope this was insightful and if you have some things to add, feel free to drop a comment!
よい一日をね（⌒▽⌒ゞ
xx Jupiter
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