So, you decided that you want to stay in Japan short term,huh?
3-5 years in Tokyo? Looking to 'find yourself'? Trying to get a hot Japanese girlfriend?
Well, those are all..uh... interesting reasons, I guess.
Anyway, here are some tips for you.
1: I stated this before, but learn the language. Of course, 3-5 years is not enough time to become fluent or anything, (well, I guess that depends on you) but if you are planning to live and work and eat etc etc, you should definitely get past basic greetings and 'Where is the bathroom?'.
2: Where ever you live, be SURE to learn what the rules are. For example, in Japan every city has different rules about garbage and stuff like that. If you don't follow the rules exactly, they will hunt you down and ask you why you didn't. (Happened to a friends of mine)
3. Get used to staring. If you are Asian, then this might not be such a problem. Most of the time, people will assume that you are Japanese and even if you can't speak Japanese, they will just assume that you are Japanese but grew up in a foreign country. (The same friend I mentioned above is a Chinese guy from Toronto. People always asked him how long he has been 'back in Japan' lol)
If you are White or Black or some kind of non-Asian looking person, then people will look at you like you have a third arm growing from your forehead.
4. PAY YOUR TAXES!! A lot of foreigners who come here for only a few years think that they don't have to, for some reason. I guess in practice, if you don't pay for like 3 years and then go back home, nothing will happen to you. But, if you decide that you want to stay longer, they won't renew your Visa, citing how you refuse to pay your taxes so you have no reason to stay in Japan. So, just to be on the safe side, please pay them.
5. Know your priorities. Japan is a great country with lots to offer, but everything is expensive. So, you need to decide what it is you want. If you want to eat high quality food, then you won't have money left for anything else. If you want to travel or go shopping, then you'll have to eat Ramen for weeks on end. You just need to decide what it is you want.
If you dare, you could try playing Pachinko (kind of a Japanese casino). You'll probably end up wasting money, but if you are lucky (like I was) then you can get a lot of money and then just quit before you get hooked.
6. Finally, STAY AWAY FROM ROPPONGI!! Roppongi is a place that is crawling with foreigners. Now, that by itself is not a bad thing, but they only foreigners who go there are the scumbag nasty, don't-fit-in-in-their-own-country-so-they-came-here type. If you go there, there is a chance that you will catch the 'disease'. (The douchebag-foreigner disease). So, I HIGHLY recommend you stay away from there. (As a side note, if you DO happen to go there, maybe just once or something, stay away from the girls there. TRUST ME! They are succubus-viral-plagues. To use a famous joke, they really are like the town bicycle, if you catch me drift)
.So, I hope this has been a little informative.