Rice is the most important component of sushi. In fact, the word "sushi" refers to the vinegared rice used for the Japanese dish. If you want to make decent sushi at home, you need to know how to prepare the rice first.
In this video, from the ChefSteps YouTube channel, chef Taichi Kitamura of Sushi Kappo Tamura demonstrates the best method for cooking and handling rice. For starters, make sure you're working with short-grained sushi rice. Each grain is smaller, plumper, and stickier than normal rice. And make sure you're using a rice cooker. You can cook rice other ways, but rice cookers cook every grain evenly.
When you're ready to get cooking, begin by washing the rice in cold water until you remove all the starch and the water runs clear. Then, soak the rice in the correct portion of water - per your rice cooker's instructions - for 15 minutes. This keeps the rice from expanding too quickly and getting mushy. While it cooks, make the sharizu vinegar seasoning using nine parts rice vinegar, four parts sugar, and one part salt.
Cook the mixture on medium heat until it all dissolves. When the rice is cooked, dump it into a bowl, remove the crispy bottom layer, and puncture the rice with your paddle. Now pour in the sharizu, one ounce of seasoning per each cup of cooked rice, and mix it together. If you keep the paddle moist with a wet washcloth, you'll avoid rice stickiness. When it's all mixed, wrangle any stray grains in the bowl and cover the rice with a wet towel until you're ready to use it.