No matter where you travel to, there are probably going to be specific customs around drinking and serving guests. Japan is no different. In Japan, it's customary for one person to pour everyone else's drink before having their own drink poured by someone else at the table. This means that it's considered rude to pour your own drink, even if you're the one pouring for everyone else at the table and you pour their drinks first.
After all of the drinks are poured, it's time to enjoy, which usually starts off with "kanpai," which is basically the Japanese version of cheers. After this is said, then it's okay to enjoy your beverage.