When drinking alcoholic beverages, it is customary to serve one another, rather than serving yourself. You should periodically check your friends' glasses, and replenish them before they are empty. Likewise, if someone wants to serve you, you should drink to make room in your glass if it is full, hold it up for the person while they pour, and then take at least one drink before putting the glass down. These customs apply to everyone in your party even if they are not drinking alcohol.
At the beginning of a meal or drinking party you should not start drinking until everybody at the table is served and the glasses are raised for a toast, which is usually "kampai". Other toasts are acceptable, but avoid using "chin chin" when making a toast, since in Japanese this expression refers to the male genitalia.
While it is considered bad manners to become obviously drunk in some formal restaurants, for example in restaurants that serve kaiseki ryori (Japanese haute cuisine), the same is not true for other types of restaurants such as izakaya, as long as you do not bother other guests.