Everybody wants to live a long, healthy life. In a new book, The Longevity Project, psychology professors Howard S. Friedman and Leslie Martin dig for clues in data collected by psychologist Lewis Terman for a study beginning in 1921 that tracked the lives of 1,500 people, from childhood to death. What do the study's findings tell us about living longer? Here are five of the secrets to longevity the authors identified:

1. Be conscientious
There are "no magic potions" to guarantee living to a ripe old age, says Laura Landro at The Wall Street Journal. The closest thing might be "a quality best defined as conscientiousness." Subjects in the study who, as children, displayed what the authors described as "persistence, prudence, hard work," and a close involvement with others were less likely to develop dangerous habits. Such people are, in the authors' words, "somewhat obsessive and not at all carefree" — contradicting the notion that being relaxed is the secret to long life.

2. Find happiness in your marriage
The conventional wisdom says married people live longer. That's true — provided you're a man in a good marriage who has traits that make you well-suited to the institution, says Friedman, as quoted by The Atlantic. Meanwhile, "Women who got divorced often thrived," Friedman said, especially if they were getting "rid of troublesome husbands." But men who divorced and never remarried often wound up in a early grave.

3. Turn that smile upside down
"Cheerfulness can kill," says Emily Yoffe at Slate. Bright-eyed, optimistic children were more likely to be highly social, and "went to more parties where they smoke and drank, craving the buzz," Yoffe says. "They died from accidents." Or they remained happy when things were going their way, then crashed when confronted with the difficulties of life. Partly due to this inability to cope, "cheerfulness was as big a risk factor for premature death as elevated blood pressure and high cholesterol."

4. Hope your parents stay together
One of the most important factors in predicting longevity is (more or less) beyond your control — the success or failure of your parents' marriage. Broken families can have devastating effects on a child's long-term health. "Parental divorce during childhood emerged as the single strongest predictor of early death in adulthood," says Landro at the Journal.

5. Keep working
Many of the long-lived, successful professionals in the study worked, at least part time, well after they reached retirement age. We're conditioned to think that stress kills. And that held true for those who showed promise as boys but ended up in "low-status jobs — streetcar conductor, baker, porter." The frustration they endured made them less likely to live to 60 than their counterparts who ended up in high-status, high-pressure jobs. "Success, even in challenging jobs with demanding hours and responsibility, is a tonic," says Yoffe. And as Friedman puts it: "Fun can be overrated."

Sources: The Atlantic, Wall Street Journal, Slate