Every sushi chef worth his weight in bluefin knows these rules. Is he going to hate you if you don't follow them? Maybe, maybe not. But do you really want to get on the wrong side of the guy with the big, sharp knife?
  1. Always fold your oshibori.
    The oshibori — ahat warm wet towel — you get prior to yoru sushi meal? Use it. But then roll it up afterward so when it's taken away, it looks as neat and tidy as it did when you received it. Some restaurants let you hang on to the cloth for your whole meal, so you can wipe your fingertips if eating with your hands.
  2. Never pour your own drink.
    It's customary to serve others, and bad form to serve yourself. If you're running low on sake, ask your companions if they need more, and rely on them to return the favor.
  3. Be judicious with your soy sauce.
    The saying that sushi is 90% rice and 10% fish isn't an exaggeration: in Japan, rice is everything. So don't fill your soy sauce dish with more than a few drops — if you overpour your sauce, you're saying the chef hasn't seasoned his rice or fish properly.
  4. Never dip rice-first.
    Always dip your nigiri in soy sauce fish-side in. The rice will absorb too much, overpowering the carefully balanced flavor of the dish. If your nigiri comes pre-sauced, don't dip it in soy sauce at all You don't want to make the chef think you don't have faith in his abilities (Also make sure no stray pieces of rice are floating in your soy sauce — it's considered very insulting to the chef!)
  5. Treat wasabi with respect.
    If you're eating nigiri, your fish probably already has some wasabi on it, added by the chef. If you'd like your bite spicier, use your chopsticks to add a little dab. Same goes for rolls: taste it first, then add a small amount to each bite. Don't ever stir it into your soy sauce!
  6. Consider ginger a palate cleanser
    Don't treat the pickled ginger that comes with your sushi the same way you would the soy sauce or wasabi, putting it directly on your sushi. It's for refreshing your palate between pieces or courses, so each bite gets to shine.
  7. Eat your sushi right away.
    If you'e sitting at a sushi bar and the chef is cutting and placing your nigiri to order, take a break from your conversation and eat your piece as soon as he puts it in front of you — the rice and fish are at precise temperatures, and the chef is probably also waiting to watch you eat the piece.
  8. Each piece of sushi is one bite. Put it all in your mouth at once.
    Suggested by @sharris