What are the best things to try for a first timer at a sushi restaurant to get a good introduction to the cuisine and be eager to return?

Tuna sashimi. It was the first thing I ever tried, and although it is raw in the middle like a rare steak, it is seared on both sides. Once I learned that tuna sashimi is delicious, I was ready to try a California roll, and once I learned that was delicious I went on to try every kind of Maki roll, and, except for barbecued eel, they are all delicious. Soon I was able to go to a sushi restaurant and eat raw fish, plain. It's not bad at all.