Drink plenty of water.
Wash your hands.
Don't share water bottles, lip balm, eye drops, or anything else that come in contact with any bodily fluid (insert your own joke here).
Wash your hands.
Cover your mouth with your arm (not your hand) if you sneeze or cough.
Wash your hands.
Use an alcohol based hand sanitizer, but make sure you rub your hands together until they are completely dry.
Drink more water.
And finally... Wash your hands...
Keeping your body healthy with vitamins, etc is important, as is keeping your body hydrated. However, the best thing you can do is prevent the transmission of the virus/bacteria. Even something as small as not sharing your pencils can make a difference (you cough on your hands, someone else picks up your pencil and puts it in their mouth, instant contamination). Don't feel bad about reminding people about washing their hands or using hand sanitizer. Keep some next to the pencils and kleenex if you have to.