If you want to have the longest, healthiest life possible, you should never have lit that first cigarette. Never stepped foot inside a fast-food restaurant or driven somewhere you could have walked. Never let yourself get those nasty sunburns.

If you did, take heart. There’s still plenty you can do to add years to your life.

“Most things I would say are common-sense, things you were taught in first grade,” said Dr. David Johnson, chair of internal medicine at the University of Texas Southwestern Medical Center.

So listen up. These 10 ways are easy and have more significance than most of us realize. At the very least, “they allow you to live more healthily in a much more psychologically satisfying life,” Johnson said.

1. Floss

Flossing removes plaque, the bacterial film that forms along your gum line. Get rid of bacteria, and you lessen your chances of heart disease, stroke, diabetes, Alzheimer’s disease and some forms of cancer, said Dr. Larry Korenman, a Texas dentist. “Oral bacteria can create proteins that are found in artery walls and in the bloodstream,” he said, “causing blood to clot more easily.” Only 5 to 10 percent of Americans floss daily.

2. Get a colonoscopy

“It’s a great test,” said Dr. Radhika Vayani, an internist at the University of North Texas Health Science Center in Fort Worth. “The 24-hour prep is the worst. … But you won’t feel the procedure. If they see a polyp, they get rid of it right then and there. That could save you from having colon cancer in five years.”

Nine of 10 people whose colon cancer is discovered early will be alive in 10 years, according to the American Cancer Society.

3. Stop eating before you’re full

Most Americans eat and eat “till we’re so full we’re about to be sick,” said Vayani. “But it takes the body 15 to 20 minutes to say, ‘You’re full.’ ” Being 100 pounds overweight can subtract a decade from your life, an Oxford University study found.

4. Use sunscreen

In a Centers for Disease Control study, only 32 percent of adults reported usually applying sunscreen. Yet this year in the U.S., 3.5 million people will get skin cancer and 76,000 more will develop melanoma, says the American Cancer Society. Every hour, someone will die.

5. Stop smoking

Yes, despite mounds of evidence it’s bad, “tons of people smoke. If you quit at age 30, you can increase your life by 10 years,” Vayani said. Quit at 40? Add nine years. 50? Six years. 60? Three.

6. Sleep

Not getting enough has been linked to memory problems, hearing problems, anger, high blood pressure, stroke, depression, vehicle accidents and obesity. A decades-long international study of 1.3 million people found “unequivocal evidence of the direct link” between lack of sleep and premature death.

7. Move

“Exercise has been demonstrated over and over to be useful,” Johnson said. “Walking gets you outside, and some outside is good as long as you don’t overdo it. The best way to get vitamin D is sunshine.”

8. Eat produce

Benefits abound. Among them: Eating five or more servings a day reduces your risk of stroke by 26 percent, according to a study reported in Men’s Health.

9. Cultivate healthy relationships

Spending time with family and friends is “psychologically helpful,” Johnson said, adding that it “isn’t a cure-all; it won’t counteract a McDonald’s cheeseburger.”

Vayani said, “If you have people in your life who are negative, who are pulling you down, you have to get rid of that relationship. It affects you more than you realize.”

10. Be grateful

“We experience great things all day long that we fail to acknowledge,” Johnson said. “Our health is more than just physical health. I see dozens of people who have illnesses that would lay you or me low, but they seem totally happy. How in the Sam Hill can that be? They’ve chosen to look at the good instead of the challenges.”