Hydrate. General good health practices keep your body strong and ready to fend off cold germs and the flu virus. And that includes drinking plenty of water. In fact, one recent study found that staying hydrated may boost a particular immune response to enable your body to better fight the viruses. Stay hydrated by drinking a lot of fluids, especially water, and by avoiding caffeinated drinks. Shoot for six to eight glasses of water per day, more if the weather is hot, says Elder.