The miserable symptoms of a cold or the flu are actually signs that your immune system is working to fight off an offending virus.  Your immune system is your best defense against infectious illnesses, according to Harvard Health Publications' HealthBeat. Keep it in optimum shape with healthy living strategies such as these:

     •Don't smoke. If you already smoke, try to quit, even if you've been unsuccessful
      at kicking the habit in the past.

     •Eat a diet high in fruits, vegetables, and whole grains, and low in saturated fat.

     •Take a multivitamin if you suspect that you may not be getting all the nutrients
      you need through your diet.

     •Exercise regularly.

     •Maintain a healthy weight.

     •Control your stress level.

     •Control your blood pressure.

     •If you drink alcohol, drink only in moderation.

     •Get adequate sleep.

     •Take steps to avoid infection, such as washing your hands frequently and
      cooking meats thoroughly.

     •Get regular medical screening tests for people in your age group and risk category.