First and foremost it is important to know that use of both chopsticks as well as fingers while eating is acceptable. Sushi was originally called a finger food because it was meant to be a quick, on-the-go snack that could be eaten quickly. Hence, it is completely acceptable to pick your sushi with your hands instead of using chopsticks. However, avoid asking for forks and knives in a sushi restaurant as this can be construed as insulting and ignorant.
If you need to dunk your sushi into soy sauce, then do so lightly. Only the fish part needs to be dunked in to the sauce, not the rice part. Dunking the rice into the sauce will cause it to fall apart. Do not use excessive soy sauce as this may imply that the original flavours were not strong enough and hence other ingredients needed to be added. If you ask for wasabi as well as soy sauce, avoid mixing it together to form a soup as they are different flavours that are not meant to be blended together.
The sushi needs to be eaten in one bite, at the most it can be eaten in two bites. However, do not place the unfinished bits of your sushi back into the plate. If you eat your sushi in two bites, hold the unfinished bit in your hand or in the chopsticks. Placing it back in the plate is considered rude. Chew your sushi with your mouth closed.
Never stick your chopsticks in your rice bowl. This is akin to a funeral rite and hence is considered offensive in a restaurant environment. Similarly, never pass food from one chopstick to another. This is also similar to a funeral rite where family members pass the bones of the deceased from chopstick to chopstick. It is however alright to move food from one chopstick to another plate.
It’s easy to forget that 65 years ago Japan was a war-torn nation. Food was so scarce that many people had to resort to eating grasshoppers along with whatever else they could find. It is therefore, considered insolent to waste even a single grain of rice. Hence it is imperative that you clean your plate and make sure every last grain has been eaten.
Lastly, never pay your bill to the chef. In the sushi culture, people who handle the food are not supposed to handle anything else, even money. Hence get another restaurant employee to assist you with the payments.