Eat more vegetables, add garlic, onion, herbs and spices to your foods, drink more green teas, etc. In general make sure you take in more phytochemicals because many of them have anti-bacterial traits, like for example allicin, found in garlic. Chicken soup is known as Jewish penicillin for that same reason, phytochemicals. Often forgotten because they do not supply any energy but they're very important for our well being.