Well, of course, the key is that the trip should be well planned before flying the country. It means purchasing JR pass is a must if you want to travel around major cities instead of spending your money on taxis. I committed to myself not to take a single taxi trip while I was there, and I was glad I did. You can go to my post in this forum for further discussion on JR Pass.
Plan your trip before hopping on & off public transports.
Planning your trip from A to B is essential so you can save time and money. A good train route app is the one with real-time train timetables including the transits, the duration of the trip, the departure and arrival of time and platform, and route options. There are so many apps out there. Japan Travel - route, map, JR, developed by NAVITIME Travel, is pretty accurate and user-friendly when I was in Japan. This app helped me plan my trip beforehand and can be used throughout Japan. You can rely on asking people the direction. You'll be surprised by how the Japanese gave their best to help you even with the broken English. I enjoyed having a little chit chat with anyone on the trains. I encountered school kids to senior citizens as long as you're polite and unassertive as well as giving them a little privacy by not crossing the line. You're in Japan. Let say, like the French in Europe who are proud of their language and hundred of years old culture and tradition, Japanese are the Asian version of it.
Secondly, you know where the right cheap places to eat? Seven-Eleven and convenient stores in Japan sell cheap good quality food. You'll be surprised at what you find in the shop. Tiny shops at the stations are always good options. I don't stick to recommended eating places from youtube channels or travel books. When you travel to the country for the first time, you don't want to lose the moment only searching for those must-visit restaurants. You want to enjoy the moment experiencing Japanese traditions and culture. Millions of them sell cheap meal with excellent taste and quality. Japanese are well-known for being attentive and detailed with their food without compromising its quality. Don't miss tiny shops along Shinjuku shopping arcades. They usually sell cheap bento boxes late afternoon, the ones that didn't make it through the lunchtime. It's an absolute bargain. I found the best ramen in a restaurant in Shinjuku designed for those who come by her/himself. Check out the story 'Ramen For A Loner'.
I love having those assorted stuffed rice balls as my snack and grabbed a bowl of salad to come with them. I spent my money, preferably in travelling experience than in eating experiences, such as ticket purchases for museums, temples, shrines, Geisha performances at Gion Corner Kyoto, and many more. Once a week, I would treat myself to fancy bars, such as Atlantis in Gion district Kyoto. Their staff are amicable, and I learnt my Japanese while sipping a glass of martini or gin tonic. They also gave me some travel tips while I was there and I admitted they were accommodating. So I just didn't spend money on expensive food and drinks there but also experienced something new from the locals.
When you are in a rural place in Japan, such as Kawaguchiko lakes in Mount Fuji for a day trip, checking out the weather beforehand is a must. So you can rent a bike or an e-bike for the whole day instead of purchasing a day-trip bus because the bus lines aren't frequent and flexible. A day trip to Nikko, for instance, the main tourist attraction such as Nikko Toshogu can be reached within walking distance. Once you're at Toshogu, you can walk to another temple from there (All signs are both in Japanese and English). So once again, checking out the weather forecast beforehand is a must.
Upon Arrival and Departure.
I prefer Haneda airport than Narita because Haneda is closer to central Tokyo. If you stay in central Tokyo, such as Shinjuku, bus limousine is cheaper, easier and more comfortable than a taxi or trains. Remember, you're carrying luggage with you, so your mobility is likely limited. Train or metro lines trip to central Tokyo (from Haneda airport) requires changing at the station. Limousine buses run straight to central Tokyo, and they stop at major hotels, such as Hilton, and Shinjuku West Exit. So, you have to do a little bit of research to find out if you stay at those hotels or closer to the hotel. Remember to book your limousine bus ticket online a day or two before your departure (back home).