There are two tricks to good sushi rice: first you rinse the rice well to remove the excess starch; and then you coat the cooked rice in a vinegar, sugar and salt mixture. The rice can be made on the stovetop or in a rice cooker, and it can be cooked up to 5 hours in advance.
Do Ahead: The rice can be made up to 5 hours in advance. Once cool, cover with plastic wrap and store at room temperature.