Sake is enjoyed as atsukan (hot) or hiya (cold). Atsukan is served in a decanter known as a tokkuri from where you pour the sake into a shot glass called an ochoko . Hiya (also known as reishu ) is poured into a glass that sits in a masu , a wooden box. Generally at your table, the waiter will fill until the glass overflows into the box. Though there is no set way to drink, you want to be careful not to spill any. Remove the glass and drink half way. Fill the glass with the sake from the box and use the box as a coaster. It is fine to drink from the box as well.
When with company, particularly Japanese businessmen, it is good manners to fill people’s glasses but not your own. People will often refill your glass even when it is not empty. There is no need to empty it for each refill. If you’re empty and thirsty, try filling someone else’s glass so they will fill yours.