Answers (3)
Generally for health and longevity, the best is to eat a high quality diet with focus on meat, fish, vegetables (especially low starch ones), eggs, and good quality oils and fats (butter, coconut oil, other nut oils, olive oil). Avoid sugar, refined starches and wheat and highly processed vegetable oils.
It is also very important to get a good amount of sleep each night, reduce stress (exercise, massage, sauna, walking...), have a social life (go out with friends) and generally do more things that make you happy.
Hope that gives you a good starting point. If you want more specific advice for a specific condition, you would need to elaborate on your question a bit more.