You might want to tell them a list of your favorite sushi fish!
It is hard for anyone to learn how to order at a traditional sushi restaurant if you go there for the first time. Not all sushi restaurants can serve you in English either. I would recommend you to study online in advance and pick up your favorite sushi dish or bring their photos. Also, it is a good idea to tell them your budget for the day so that they can serve you within your budget. Well, after all, communication is everything! I hope you enjoy a good time!