I was born in Japan and have visited many times since then. Here are some suggestions to help you have a great time visiting an amazing country. Adding a link of my list of cities to visit in Japan: Travel - recommendations for cities to visit in Japan (and some things to do / see)
  1. Get a JR Rail Pass
    If going for more than a week and visiting more than one city, this is an unbelievable deal. Can be used on all JR lines within and between all Japanese cities, including booking Shinkansen (Bullet Train) seats. MUST BE PURCHASED OUTSIDE OF JAPAN then redeemed for the actual pass in Japan at any JR station "green window". Can even be used for the train ride to/from Narita International Airport.
  2. Have cash (Yen) but beware pickpockets
    Acceptance of credit cards has increased greatly and will work at most hotels, chain/department stores, and larger businesses. But Japan is still a cash society to a surprising extent, especially when it comes to restaurants, tourist sites, and smaller Mom & Pop shops. Fortunately, Japan is also relatively safe with low rates of violent crime but pickpockets are not unheard of.
  3. Don't tip
    Japan does not have a culture of tipping. Memorably, during the Winter Olympics in Nagano, Japan, some restaurants put tips that customer had left on their tables in their "lost & found". It's usually policy for hotel staff to have to decline tips as well and cab drivers and restaurant staff do not expect tips
  4. Bring a handkerchief
    All Public bathrooms will have sinks for washing your hands. Many will have soap dispensers. Some have hand dryers. Almost none have paper towel dispensers. A must for drying off your hands.
  5. Grab some free packets of facial tissues
    Because handkerchiefs are used to dry hands after washing, they are not used for blowing one's nose. Fortunately there's no shortage of people handing out free, promotional packages of facial tissues that can go in your pocket or purse.
  6. Visit Tourist Information Centers
    Nearly every city and town will have one, usually at or near the local JR train station. They will have free, local maps in multiple languages, helpful staff, and often sell bus passes good for entire days or multiple days.
  7. Learn a few key phrases in Japanese & don't be afraid to ask for help
    Nearly all Japanese people now grow up learning English at school. But they might be hesitant or embarrassed to use it. Breaking the ice in Japanese is polite, appreciated, and your clumsy Japanese will help them feel more comfortable with their English. "Sumimasen" is the form of "excuse me" appropriate before asking someone to ask for help. "Eigo hanase masu ka?" or "Eigo wakari masu ka?" mean do you speak/understand English. And "domo arigato" with a bow is a polite way to thank someone
  8. Bring comfortable shoes and socks without holes
    Japan has great mass transit systems but you'll still often walk significant distances within and to/from train stations and bus stops. When you get to a destination you'll often be expected to remove your shoes, especially if visiting someone's home, so you your socks will be on full display!