The easiest approach is probably to avoid or reduce obviously harmful habits and behaviors that result in chronic diseases (eg: cardiovascular disease, diabetes)
- Avoid smoking and hard drugs
- Avoid excessive alcohol consumption
- Avoid fast food, excessive salt and sugar, deep fried dishes
- Avoid excessive stress and worrying
Besides that, focus on the basics:
- Consistent and restful sleep
- Healthy, balanced diet
- Regular exercise
- Novel and mentally-stimulating activities, continuous learning
- Strong social connections (not just online social networks, but actual friends and family you can hang out with in-person)
If you want even more, there have been studies about 5 blue zones where inhabitants regularly reach ages of 100 or more, and 9 habits they follow: https://www.bluezones.com/2016/11/power-9/
1. Move naturally: build exercise into your daily life
2. Purpose: a reason to wake up in the morning
3. Downshift: Routines that shed stress
4. Only eat until you are 80% full. Consider occasionally fasting.
5. Plant and bean-based diet
6. Moderate (1-2 cups/day) consumption of alcohol
7. Faith
8. Close family connections
9. Social circles that support healthy behaviors