Sleep: it is important to get as much sleep as you can as sleep is when the body repairs the immune system
Hydration: your immune system flows through your bloodstream and you need water to make sure the blood flows effectively
Stress: reduce your stress levels as much as possible as, if we can be calm our nervous system can ramp up and do what it needs to do so that means taking time out
Nutrition: examples are viatamin C & D
Supplements: may be useful if you feel your diet is a little deficient