I am hoping you plan to keep the yellow tang longer than a year. This fish's life span is much longer than that.
The most important thing in keeping any fish alive for a long time is providing it with the appropriate tank size, ideal and stable water conditions, and a nutritious and varied diet. There should be at least 6 or 7 different types of seafood in the fish's weekly diet, and it would benefit you greatly if you are using garlic and vitamins (Zoe, Selcon, VitaChem) in the fish's food.