The four pillars of health which can optimize your immune system are:

1. Sleep- at least 7 hours of sleep a night keeps you healthy

2. Eat healthy- eat fruits and vegetables

3. Exercise- Daily doing exercise keeps you healthy

4. Avoid bad habits- avoid smoking and alcohol as it makes you more susceptible to the disease

References

https://www.cdc.gov/coronavirus/2019-nCoV/index.html