1. Get as much quality sleep as you need. Some experts say this is the single most important step you can take to keep your immune system functioning well. Trade the late show for an extra hour of rest, and don’t set your alarm clock if you don’t need to. Stay away from bright lights, computer screens, and upsetting thoughts in the hour or two before bed. It’s also wise to skip that nightcap. Alcohol might help you fall asleep, but disrupts sleeping patterns so it’s harder to get deep, restorative sleep.