Japan is a very fascinating country, but certainly very different and far from ours in terms of culture, traditions, ...
For this reason I suggest you to approach this beautiful country with an open mind and a strong will to know.
English is not widespread and little spoken even in big cities. Japanese people are very helpful, it will not be difficult to understand and be understood.
Credit cards are not accepted, cash is preferred. So think about comning with a little yen. It is also possible to withdraw cash on the spot with the ATM, using the international Maestro circuit, at the Seven Eleven supermarkets which have their own ATM for international withdrawal. Plase note that ATMs that you will find in Japanese banks are not authorized for the international ATM service.
If you intend to travel by car, remember that the guide is on the right and that you will need to hold an international driving license that you can request in Motorization offices or at a driving school that will take care of managing the entire release request process for you.
To make your stay in Japan easier and more complete, I recommend using the Free Guide service. This service puts at your disposal (in the cities where the service is running) guides who, based on your requests or a pre-established program, will take you on a guided tour of the city. The service is in English only and is FREE. Guides are generally retired or students who put their time and knowledge of the city at your disposal. The only cost to you will be the transport costs (if you use public transport) and the costs for the lunch of the guide who can choose the restaurant where to have lunch. I advise you to take advantage of this service because it will allow you to maximize your visit and to have advice for an experience from locals. Highly recommended especially if you visit big cities like Tokyo or Kyoto. Please note that the service must be booked in advance
To travel light, especially if traveling by train, use the TA-Q-BIN baggage delivery service provided by Yamato. You can find it in major airports or you can request it at your hotel in Japan. Remember also that you can also use the lockers to deposit your luggage or your purchases for a few hours while visiting the city. You can easily find them in the train or metro stations.
Last but not least, portable wi-fi. In Japan, wi-fi is widespread but not available everywhere. To be able to always have data coverage, especially when visiting cities and therefore having maps and directions available in real time, portable wi-fi is a must! There are several providers that offer devices rental. On my last trip, for which I needed constant coverage since I used my mobile phone as a car navigator, I relied on Wi-Ho. This provider offers two types of data coverage: city type, if you move within big cities or wide type if you move even in rural and less populated areas. I can guarantee that the wide type works very well, always guaranteeing you constant coverage wherever you are. The device must be rented online in advance and, at the time of booking, you can decide whether to pick it up at the airport or have it delivered directly to the hotel upon your arrival. For the redelivery I suggest you to opt for the return with mail or courier. You will be provided with a pre-paid stamped envelope that you simply need to leave at the reception of your Hotel. They will take care of sending it for you.