FIRST YOU have to get over the idea that sushi is raw fish. Nothing like oysters or clams on the half shell or even steak tartar. Second, and believe me when I tell you this, raw fish is not "fishy". It is cool, light and the flavor is subtle, but unforgettable. So what if it wiggles.
Because you are a very tolerent person, and godforbid you should ever be accused of an unwillingness to broaden your horizons, you should not be intimidated. These fish are cut into lovely clean filets, no heads thank you.
For your first sushi outing, sit at the sushi bar where you can watch the chef do his graceful act of palming the rice, cutting the fish and forming the sushi. He makes a food processor look like a lumberjack.
Order a set assortment of sushi or sashimi (small pieces of raw fish without any trappings). It is cheaper than ordering a la carte and gives you an opportunity to discover which fish you like. Salmon, tuna, flounder and other white fishes are very tender. Octopus is not. Ask the sushi chef what sort of fish you are eating. He likes to chat. In Japan, sushi bars are the local hangouts where the chef functions as a bartender/psychiarist and gossip.
The sushi will be presented on a flat lacquered tray garnished with pickled ginger, and if it is sashimi, a small round chartruse ball of burning hot horseradish (or mustard, depending on the translation). The horseradish is cut on the top in a tiny grid pattern. Watch the chef do this. It's like trying to hold a grape up in the air with two fingers and skinning it with a meat cleaver.
You will also be given a small flat dish. Pour soy sauce into the dish, and with chopsticks pinch off a piece of the horseradish and mix it with the soy sauce. Dip the sashimi into the sauce and pop it into your mouth in one bite. Sushi is picked up with thumb and forefinger and dipped into the soy sauce. When it is prepared shusi it is spread with green horseradish so unless you like it tearfully hot, dip it in unaltered soy sauce.
The Japanese think it is very funny if you try to bite sushi in half. It is rather like watching someone attack a Big Mac with a knife and fork. Not exactly gauche or rude, but amusingly ignorant. The first time I had sushi, the owner of the restaurant rushed frantically towards me and in sign language showed me how I was doing it all wrong. Just to show him I understood, I took a piece of sushi, a bit larger than the cubic capacity of my cheeks, and stuffed it in, horseradish and all. It was so big I could hardly chew it and so hot there were tears in my bugged eyes. He thought this was great and gave me a pat on the back to show I wasn't so weak after all. The chef was the happiest. It seems that even if the piece is too big for your mouth, the best way to show you can cut the mustard is to stuff it in and make the best of it.