What do you wnat to do while in Japan? It would help if you tell me what it is you want to see. But as for the basics you should try to eat the local food.
There's:
-Ramen noodles of course
-curry(the curry house thing is a good suggestion)
-takoyaki (octopus balls)
-monjya yaki (this as far as I know is only available in Japan and not yet here in the US but basically its flour and starch and you fry it and get a gooey pancake sort of thing. Looks weird but tastes great!)
-Drink! well if you are old enough.
Places to see will depends on what part of Japan you go to. Well enjoy!