Find the top causes of mortality in your area and then try to improve your risk factors for those
Get all of the available recommended vaccinations for diseases that are endemic in your area, including boosters on the recommended schedules; if it's available, always get a seasonal flu shot every year; also try to get vaccinated for pneumonia (reducing your risk of serious complications from other respiratory illnesses); get other people who live in the same household with you to get vaccinated too
If you need complex non-emergency medical care, seek it in a different country with a more advanced medical system
Try to mitigate exposure to major causes of mortality and morbidity (air pollution, contaminated water, contaminated food, violence); try to ensure that you personally live in a building with adequate ventilation, water supply, sanitation, and physical security; if your water quality is questionable, consider filtering and/or treating tap water somehow before using it for bathing or dishwashing (not just drinking)
Don't eat raw or undercooked food of any type that has a history of contamination in your area; don't wash food with water of uncertain quality
If you have any influence with any level of government, try to get them to improve sanitation (sewage, street cleaning, trash collection), air quality, water quality, and food safety inspection procedures in your area
Take exposure precautions when there is an epidemic or outbreak of contagious disease (like right now with COVID-19, but also during future outbreaks of other pathogens) -- hand sanitizer, hand washing, wearing a mask, reducing your physical contact with others, avoiding crowded areas
Find screenings for diseases that increase your risk of death (diabetes, high blood pressure, heart and lung diseases, cancers) and repeat the screenings periodically; consider getting simple devices that would let you monitor indicators for some of these at home (e.g. a blood pressure monitor)
Try to maintain and improve your fitness, nutrition, and mental health
Maintain a good social support system (family, friends, religious communities)