If there's one thing I advise against while in Japan: ordering individual drinks
If there's one word in Japanese you need to learn to experience the nightlife, it's "nomihoodai" - ????. It means "all you can drink".
For anywhere between 1000 - 2000 yen (about 10USD - 20USD), you can spend 1-2 hours drinking as much as you can.
It's somewhat magical. You order one drink...your server brings it to you...and you order the next drink before they even put the first one on the table.
But there are a few rules you should be aware of to engage in the amazingness of bars in Japan:
First, the price of your menu determines which drinks you get, with cheaper menus meaning less options. If you accidentally order outside of that menu, you'll get charged the regular price of the drink.
Second, if you take another drink before your previous one is finished and allow the server to collect that unfinished drink, you'll be charged that drink's regular price. So start chugging if your server is approaching your table!
Third, every izakaya (Japanese-style bar) is different, but they usually require one small dish of bar food per person to be ordered. These are very cheap and can be anything from fries to takoyaki - fried octopus.
As long as you stay in line with the all-you-can-drink requirements, nomihoodai will keep you partying every night in Japan. Since bars don't really seem to close until everyone leaves, feel free to do two nomihoodai in one night!