How can I give my immune system a boost?

HL123 ways to boost human immune system

1. Have a healthy and balanced diet.

2. Have Sufficient Sleep.

3. Take Dietary/Health Supplements.

4. Have a Healthy Mind.

5. Do physical exercise at latest 30 minutes a day.

Note: Items (1) to (4) are the most important things to do to make your immune system stronger, if you do not have time to do exercise. Why? I have come to this conclusion based on my personal experiences.