From the excellent book Strength to Strength: Finding Success, Happiness, and Deep Purpose in the Second Half of Life by Arthur Brooks

There are seven big predictors of being Happy-Well from the Harvard Study of Adult Development that we can control pretty directly:

1. Smoking. Simple: don’t smoke—or at least, quit early.
2. Drinking. Alcohol abuse is one of the most obvious factors in the Grant Study leading to Sad-Sick and putting Happy-Well out of reach. If there is any indication of problem drinking in your life, or if you have drinking problems in your family, do not wonder about it or take your chances. Quit drinking right now.
3. Healthy body weight. Avoid obesity. Without being fanatical, maintain a body weight in the normal range, eating in a moderate, healthy way without yo-yo dieting or crazy restrictions you can’t maintain over the long run.
4. Exercise. Stay physically active, even with a sedentary job. Arguably the single best, time-tested way to do this is walking every day.
5. Adaptive coping style. That means confronting problems directly, appraising them honestly, and dealing with them directly without excessive rumination, unhealthy emotional reactions, or avoidance behavior.
6. Education. More education leads to a more active mind later on, and that means a longer, happier life. That doesn’t mean going to Harvard; it simply means lifelong, purposive learning, and lots of reading.
7. Stable, long-term relationships. For most, this is a steady marriage, but there are other relationships that can fit here. The point is having people with whom you grow together, whom you can count on, no matter what comes your way.

According to George Vaillant (author of the study), the single most important trait of Happy-Well elders is healthy relationships….The clearest message that we get from this . . . study is this: good relationships keep us happier and healthier. Period.

Here’s a link to the study: https://www.adultdevelopmentstudy.org/

Hope this helps!