One of the best things about Japan is how completely different the culture is from that of the United States and other western countries. But that does mean learning a bit about these differences before you travel to make sure you're prepared, and not offending anyone! Here are 7 things I think it important for anyone visiting Japan to know.
Convenience Stores
Convenience stores in Japan (conbini for short), are ubiquitous, very popular, and about a million times nicer than the American version. Conbinis are a great place to stop for a snack and bathroom break when out sightseeing, as well as the best place to go for an ATM. I personally find that 7-11 ATMs work best with my American Visa card, and they have an English option. For snacks, 7-11 and Family Mart are my favorites.
Restaurant Reservations
A restaurant reservation in Japan is a strict promise to appear. Often, your card is charged for a last-minute cancellation or change in guest numbers, or your phone number is black-listed so you're not able to reserve at other restaurants in Japan. For this reason, I don't recommend making tons of restaurant reservations in Japan unless there are specific restaurants you'd like to visit. There are so many amazing walk-in options that reservations aren't necessary.
Shoes & Socks
There are quite a few places in Japan where you will need to remove your shoes - temples and shrines, the lobby of hot springs facilities, and more traditional cafes and restaurants don't allow outdoor shoes. Additionally, anywhere with tatami flooring will not allow shoes. Plan accordingly and wear or bring socks!
Cash
As technologically advanced as Japan is, cash is still the most common form of payment, even for large purchases. It's not uncommon (and is safe) to carry $400-$500 worth of yen in your wallet. Most shops and convenience stores take foreign cards, but some smaller restaurants, shops, and even most train stations (for tickets or to top up your subway card) only accept cash.
Tipping
Most service industries in Japan do not accept tips, including at restaurants and in taxis. Some more tourist-centric industries are starting to accept tips, and so for a private guide or class, or even for staff at a higher-end hotel, a 10% tip would be appreciated but is not necessary.
Luggage Forwarding/Luggage Storage Lockers
Japan has the most amazing luggage forwarding service! For $10-$15 per large suitcase, a courier service will pick up your luggage from your hotel and deliver it the next morning to your next hotel (or a later hotel - your hotel will hold your bags for you). The front desk staff or concierge can help you fill out the form and take payment for this service when you check out. If needed, there are also luggage storage lockers in nearly every train and subway station in Japan. Pay when you pick up your bags - prices range depending on locker size from less than $1 to around $5 per day.
Masks
Wearing a mask is super common in Japan, and is expected of anyone who has even a small cough as a courtesy to others. Masks don't always indicate illness either - if you don't want to do your makeup or are feeling anti-social - wear a mask!