Harvard followed 800 people for their entire lives to see what actually makes people live happier, healthier, and longer.

One of the three samples of people — 268 Harvard graduates born around 1920 — was the longest prospective study of physical and mental health in the world.

A second sample was the longest prospective study of "blue collar" adult development in the world.

The third sample was the longest prospective study of women's development in the world.

The overall study found six key factors that impact happiness and longevity, including relationships, education, and generosity.

There's a lot of good advice on how to be happier or more productive or how to have better relationships. But tips on how to improve your whole life — something that will last decades and experience countless unpredictable changes — those should be regarded with extreme skepticism.

The only way to really get some good insights would be to follow a lot of people for their entire lives and see what actually works. Luckily, somebody did ...

The Study of Adult Development combined three massive longitudinal studies — research projects that followed people from youth until old age — to figure out what makes a good life.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

The Study of Adult Development is a rarity in medicine, for quite deliberately it set out to study the lives of the well, not the sick. In so doing it has integrated three cohorts of elderly men and women — all of whom have been studied continuously for six to eight decades. First, there is a sample of 268 socially advantaged Harvard graduates born about 1920 — the longest prospective study of physical and mental health in the world. Second, there is a sample of 456 socially disadvantaged Inner City men born about 1930 — the longest prospective study of "blue collar" adult development in the world. Third, there is a sample of 90 middle-class, intellectually gifted women born about 1910 — the longest prospective study of women's development in the world ... Like the proverbial half loaf of bread, these studies are not perfect; but for the present they are, arguably, the best lifelong studies of adult development in the world.

George Vaillant is a professor at Harvard Medical School and led the study for over 30 years. His book is Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development.

With almost a century of data on nearly 1,000 people, there are plenty of insights. We'll cover 6 big ones that can get you on your path to awesomeness. (Remember: skimming my blog posts voids the warranty. If you don't read the whole thing and your life goes on to be awful, you will know why.)

Forgive me for starting with something obvious, but it had such an impact that it cannot be ignored.

1. Avoid smoking and alcohol

Among the college men studied, heavy smoking was ten times more frequent among the "prematurely dead" than among the "happy-well." REUTERS/ Daniel Munoz

Hi, my name is Eric and it was never my intention to write after-school specials but here we go: Kids, smoking is bad.

It was the #1 predictive factor of health.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

In both male cohorts not being a heavy smoker before the age of 50 was the most important single predictive factor of healthy physical aging. Among the College men heavy smoking (more than a pack a day for thirty years) was ten times more frequent among the Prematurely Dead than among the Happy-Well. Yet if a man had stopped smoking by about age 45, the effects of smoking (as much as one pack a day for twenty years) could at 70 or 80 no longer be discerned.

And drinking too much doesn't only hurt your health. Over the long haul it makes you less happy and screws up relationships.

Some people drink because they have problems. But the study showed alcohol is also an independent cause of problems, not merely a result.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

... prospective study reveals that alcohol abuse is a cause rather than a result of increased life stress, of depression, and of downward social mobility ... Alcohol abuse — unrelated to unhappy childhood — consistently predicted unsuccessful aging, in part because alcoholism damaged future social supports.

Maintaining a healthy weight increased lifespan and regular exercise boosted both longevity and happiness. Plain and simple: those things you know you're supposed to do to stay healthy? Do them.

(To learn more about the science of a successful life, check out my bestselling book here.)

Okay, obligatory obvious stuff out of the way. You have to keep yourself healthy. But you also have to keep your brain healthy. And maybe not for the reasons you might guess.

2. Years of education = good

The study found that pursuing more education led to better habits and healthier lives. Paul Marotta/Getty

It's probably no surprise that, on average, the Harvard men were healthier at age 70 than the underprivileged men. But here's the twist...

If you compared only the guys from both groups who attended college, the difference vanished.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

... the physical health of the 70-year old Inner City men was as poor as that of the Harvard men at 80. But remarkably, the health of the college-educated Inner City men at 70 was as good as that of the Harvard men at 70. This was in spite of the fact that their childhood social class, their tested IQ, their income, and the prestige of their colleges and jobs were markedly inferior to those of the Harvard men. Parity of education alone was enough to produce parity in physical health.

This wasn't due to family income and it wasn't due to IQ. Pursuing more education led to better habits and healthier lives.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

The components of education that appeared to correlate with physical health in old age were self-care and perseverance — not IQ and parental income. The more education that the Inner City men obtained, the more likely they were to stop smoking, eat sensibly, and use alcohol in moderation.

(To learn the two-word morning ritual that will make you happy all day, click here.)

Okay, prepare yourself: the next one can be a little sad for some people because we can't change the past ... or can we?

3. A happy childhood

The study found that "what goes right in childhood predicts the future far better than what goes wrong." Win McNamee/Getty

How much someone was loved as a child predicted their adult income better than knowing what social class they were brought up in.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

... for both the Inner City men and the Harvard men the best predictor of a high income was not their parents' social class but whether their mother had made them feel loved.

Many say that you can find out what someone is really made out of by seeing how they handle a really stressful situation. The Study of Adult Development found that the people who aged the best had coped well with something so horrific you wouldn't wish it on your worst enemy:

Adolescence.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

Again, as I have followed the lives of the Inner City men, one of the best indicators of successful aging was how well they had adapted in junior high school. Of the 150 Inner City men with the best scores for coping in junior high school, 56 were among the Happy-Well and only 13 were among the Sad-Sick. Of the 19 Inner City men with the lowest scores for adolescent adaptation, only a single man was among the Happy-Well, and 11 men, three-fifths, were among the Sad-Sick or Prematurely Dead. Successful adolescence predicted successful old age.

Yes, all this kinda sucks for some people. Amazon doesn't sell Time Machines and me saying, "Well, you should have picked your parents better" is far from helpful. So if your childhood was less than perfect and your adolescence felt like a bad reality show, does this mean you're doomed?

No. What went right in childhood was much more predictive than what went wrong.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

A warm childhood, like a rich father, tended to inoculate the men against future pain, but a bleak childhood — such as with a poverty-stricken father — did not condemn either the Harvard or the Inner City men to misery ... Perhaps the best summary statement is, What goes right in childhood predicts the future far better than what goes wrong.

And there's even more reason for hope. Sometimes love and support come late — but that can be enough to heal old wounds.

When people found a loving spouse or trusted friends in adulthood, the damage of a tough childhood could be undone.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

It is not the bad things that happen to us that doom us; it is the good people who happen to us at any age that facilitate enjoyable old age ... For women, as well as for men, spouses could sometimes heal dysfunctional childhoods ... A good marriage at age 50 predicted positive aging at 80 ... After following disadvantaged Hawaiian youth for almost half a century, Emmy Werner explained that "the most salient turning points ... for most of these troubled individuals, however, were meeting a caring friend and marrying an accepting spouse."

We need love at every age. A warm childhood is a great blessing but, as with so many other things in life: "better late than never."

(To learn 5 secrets from neuroscience that will increase your attention span, click here.)

So if the study found one big thing you damn well better remember, what was it?

4. Relationships are everything

The study found that people aged successfully when they gave to others joyously and received from others gratefully. Shutterstock

Plenty of the men and women who had smarts and family wealth didn't fare well. And many who had fewer advantages did just fine. It was people's ability to deal with others that made the biggest difference.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

The lives of all three cohorts repeatedly demonstrated that it was social aptitude — sometimes called emotional intelligence — not intellectual brilliance or parental social class that leads to a well-adapted old age. .... successful aging means giving to others joyously whenever one is able, receiving from others gratefully whenever one needs it, and being greedy enough to develop one's own self in between.

What's one of the biggest mistakes we make when it comes to relationships? Not working hard enough to create new ones when the old ones fade away.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

Successful aging requires continuing to learn new things and continuing to take people in ... a widening social radius at age 50 was just as important to successful psychosocial aging as emotional maturity.

Asked to summarize the results of The Grant Study (the Harvard group), Vaillant simply replied, "Happiness is love. Full stop."

(To learn 3 secrets from neuroscience that will help you quit bad habits without willpower, click here.)

So what separated those who succeeded with others from those who failed? It ended up being one of the most powerful predictive factors in the study.

5. Coping skills

Bad coping behaviors, like pouting and blaming others, sooth bad feelings in the short term but wreak havoc in the long term. REUTERS/Eric Vidal

Using "mature defenses." Basically that means how you respond to the painful thoughts and feelings produced by difficult people and this occasional horror show called life.

When things don't go their way, teenagers scream and pout and blame everyone but themselves. However, when people become adults well, sometimes they still scream and pout and blame everyone but themselves.

And this does not lead to good things. How you cope with the inevitable problems of life has far-reaching, long-term consequences.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

... In both samples mature defenses were common among the Happy-Well and virtually absent among the Sad-Sick.

Blaming others, being passive-aggressive, living in denial, acting out and retreating into fantasy were all maladaptive coping mechanisms associated with poor outcomes. These behaviors soothed bad feelings in the short term and wreaked havoc in the long term by ruining relationships and producing lousy life decisions.

Those who thrived chose more mature methods of coping like altruism, sublimation, suppression and humor.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

These four mature coping strategies are not only associated with maturity, but they can be reframed as virtues. Such virtues can include doing as one would be done by (altruism); artistic creation to resolve conflict and spinning straw into gold (sublimation); a stiff upper lip, patience, seeing the bright side (suppression); and the ability not to take oneself too seriously (humor). These latter behaviors are the very stuff of which Victorian morality plays are made and they provide antidotes to narcissism.

Adolescence always ends but, sadly, self-absorbed, attention-seeking adolescent behavior can continue long into old age. For some people it reaches truly tragic, pathological extremes like blogging.

(To learn the 5 questions that will make you emotionally strong, click here.)

So if you learn to use mature coping skills and don't act like a selfish brat, you're ahead of the game. But those who truly thrived took it to whole 'nother level.

6. 'Generativity'

The best way to selfishly improve your life is to focus on helping those around you. FreeBirdPhotos/Shutterstock

Bottom line: "generativity" is giving back.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

Generativity means community building. Depending on the opportunities that the society makes available, Generativity can mean serving as a consultant, guide, mentor, or coach to young adults in the larger society. Research reveals that between age 30 and 45 our need for achievement declines and our need for community and affiliation increases.

When we're young, we're all a little selfish. And that's okay. We need to figure the world out, we need to figure ourselves out and we need to build a life.

But when that is done, the best way to selfishly improve your life is to be unselfish and focus on helping those around you.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

Among all three samples generative men and women at 50 were three to six times as likely to be among the Happy-Well in old age as among the Sad-Sick ... In all three Study cohorts mastery of Generativity tripled the chances that the decade of the 70s would be for these men and women a time of joy and not of despair.

Spend your first few decades building a good life and a well-rounded self — and then spend the remaining decades sharing with others what you have gained and learned.

(To learn the 4 secrets to reading body language like an expert, click here.)

Okay, we've covered a lot. Let's round it all up and learn what effect the big six actually have

Sum up

This is how to make your life awesome:

• Avoid smoking and alcohol: Duh.

• Years of education = good: Education seems to increase good habits (and being surrounded by smart, ambitious people never hurts).

• Have a happy childhood: It's huge. And surrounding yourself later in life with people who love you can help repair a difficult youth.

• Relationships are everything: "Happiness is love. Full stop."

• Mature coping skills: Stop projecting and stop being passive-aggressive. Use mature defenses like humor when life gets hard. (Yes, immature humor is still mature coping. You're welcome.)

• Generativity: Build a good life, a well-rounded self and then give back.

George Vaillant spent so long interviewing people who were receiving Social Security checks that by the time he finished, he was receiving them, too.

His father had been an archaeologist, an arena that he had no interest in. But looking around at the stacks and stacks of reports covering literally thousands of years of people's lives, he realized, in a way, he'd become an archaeologist too.

His book contains a startling number of insights into what does (and decidedly does not) create a good life. We covered the big ones. So what would happen if you could tell good ol' George your personal score on the above six recommendations?

On average, he'd be able to predict your health and happiness for the next thirty years.

From Aging Well: Surprising Guideposts to a Happier Life from the Landmark Study of Adult Development:

The protective factors a stable marriage, the ability to make lemonade from lemons, avoiding cigarettes, modest use of alcohol, regular exercise, high education, and maintaining normal weight — allow us to predict health thirty years in the future.

None of the above pieces of advice was "inherit a billion dollars" or "win the Olympic gold medal in ice dancing." They're things we all can do, even if that means forming new relationships or taking some college classes at night.

A good life is not outside your reach. It will take some effort — but you knew that, right? The important part is that it's in your control. Frankly, George said it best:

"Whether we live to a vigorous old age lies not so much in our stars or our genes as in ourselves."