Every part of your body, including your immune system, functions better when protected from environmental assaults and bolstered by healthy-living strategies such as these: Don't smoke. Eat a diet high in fruits, vegetables, and whole grains, and low in saturated fat. Exercise regularly.Maintain a healthy weight.very part of your body, including your immune system, functions better when protected from environmental assaults and bolstered by healthy-living strategies such as these: Don't smoke. Eat a diet high in fruits, vegetables, and whole grains, and low in saturated fat. Exercise regularly. Maintain a healthy weight.