1. Do all your research before you leave home
Research everything you need in your own language and bring it with you in a convenient form for use in Japan, addresses, phone numbers, stations, etc. Photocopy sections of books, maps, etc.
2. Convert your money into Yen before you arrive
To have yen with you when you arrive is good for many reasons.Your credit cards may not work in ATM's and if a machine eats your card, you may have no way to get it back. Leaving you with no credit card at all! Also you may arrive in Japan at a time when everything is shut, banks and money exchange.
3. Pack light
You will quickly find that Japan with a big suitcase is no fun. Steps, escalators, lifts, gutters, platforms, sidewalks all take their toll on the weary traveller. So take a small suit case with a small day pack & buy a suitcase while in Japan and fill it up with all the great stuff you find when out shopping.
4. Dress conservatively
Foreigners already stand out a lot in Japan so no need to add to that with wild clothes. Plain neutral colours will allow you to fit in better whether it be on the train, bus or on the street. For business only take white shirts.
5. Talk calmly, slowly and quietly
Japan is a noisy place but its mostly from machines not people. Trucks, trains, signals at pedestrian crossings, etc. In trains particularly, its as quiet as a zen meditation and you will fit in if you observe the mood in the situation. If you can't speak Japanese its ok, but you will have to be calm, patient and quiet as you explain yourself & your needs in English.
6. If you have special needs items bring them
If you eat special foods, take certain medicines please bring them with you to Japan in adequate quantities, all medicines with a doctors note. Make sure everything is in original packaging. Why, you could probably find the same or similar in Japan but do you have the time or money to find it?
7. Bring slip on shoes
If you don't have any slip on shoes now is the time to invest in some. While in Japan, western style shoes, particularly lace up style shoes will slow you down. So a good investment is slip on shoes particularly if visiting a Japanese house, bath house, traditional restaurant,etc.
8. Always arrive early
In Japan, particularly the big cities like Tokyo, you will find yourself in new surroundings. So it takes time to find your way around, get use to, get your bearings, etc. So a good tip is to always give yourself plenty of time to get a place, find it and relax. Being early is ok, but being late is frowned upon.
9. Always carry an empty plastic drink bottle, and a disposable pack of tissues with you
Commuting & travelling in Japan is thirsty work. Buying drinks continuously all adds up so take your own container and fill up along the way. Tissues are handy when there is no toilet paper. Always be prepared!
10. Bring plenty of high quality, but lightweight gifts from home to give to new friends
You will get the chance to meet many people and to leave a good impression, return a favour or share a memory a gift is an ideal way to do it. In most cases your Japanese hosts will shower you with gifts and you will need to reciprocate.