Japanese Dining Etiquette for Drinking
Meals are often accompanied with drinks, either beer or sake -- don't drink alone! Wait on all glasses to be filled, then someone will give a toast or simply say kanpai! which means cheers. Raise your glass, return the kanpai, and then drink.
Japanese often jump at the chance to pour drinks for each other; you should do the same. Top up the glasses of people seated around you, and never pour your own drink.