If you want to have the longest, healthiest life possible, you should never have lit that first cigarette. Never tasted that first cheese fry. Never stepped foot inside a fast-food restaurant or driven somewhere you could have walked. Never turned up your nose at vegetables or 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, things you were taught in first grade,” says Dr. David Johnson, chair of the department of internal medicine at the University of Texas Southwestern Medical Center. “You don’t have to go to medical school to figure out things are bad for you like smoking, being a sloth.”

So listen up. These are easy ways and have more significance than most of us realize. Truth to tell, Johnson says, “Collectively, even if they don’t let you live longer, they allow you to live more healthily in a much more psychologically satisfying life.”

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, says Dr. Larry Korenman of Loveable Smiles in Richardson.

“Oral bacteria can create proteins that are found in artery walls and in the bloodstream,” he says, “causing blood to clot more easily. Infection in the mouth can cause its own small blood clots, which can enter the bloodstream.”

Years added? More than six if you floss daily (which only 5 percent to 10 percent of Americans do), writes Dr. Michael Roizen in RealAge.

Get a colonoscopy

“It’s a great test,” says Radhika Vayani, an internal medicine doctor of osteopathy at the University of North Texas Health Science Center in Fort Worth. “The 24-hour prep is the worst. You basically drink nasty stuff, and you have diarrhea. 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.”

Years added? Lots. Nine out of 10 people whose colon cancer is discovered early will still be alive in 10 years, according to the American Cancer Society. Many will live a normal lifespan.

Stop eating before you’re full

Most Americans eat and eat “till we’re so full we’re about to be sick,” says Vayani. “But it takes the body 15 to 20 minutes to say, ‘You’re full.’”

Years added? Being 100 pounds overweight can subtract a decade from your life, according to an Oxford University study. So it stands to reason that maintaining a healthy weight and thus reducing your risk for diabetes, heart disease and various other unpleasantries would add at least some precious time to your life.

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 from that deadliest form.

Years added? Possibly 20. The CDC study reported that someone who died of melanoma between 2000 and 2006 died two decades prematurely. Although the sun doesn't cause all melanomas, it does cause most.

Stop smoking

Yes, despite years and years of evidence proving all the nasty stuff it causes, “tons of people smoke,” Vayani says.

Years added? "If you quit at age 30, you can increase your life by 10 years," she says. Quit at 40? Add nine years. 50? Six years. 60? Three.

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, according to sleepbetter.org.

Years added? Hard to say, but if someone died in a car accident caused by sleep deprivation, for instance, that's probably several decades.

Move

“Exercise has been demonstrated over and over to be useful,” Johnson says. “Truth is, any level is of value.” Walking, he says “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.”

Years added? At least three years. That's the number from a study reported in The Lancet for people who exercised even 15 minutes a day.

Eat produce

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

Years added? Webmd.com reports that Seventh-day Adventists, who typically follow a vegetarian diet, outlive those who don't by three to seven years.

Cultivate healthy relationships

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

Vayani tells patients, “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.”

Years added? Nothing specific, but "studies have shown that people with more friends and people in healthy relationships live longer," she says.

Be grateful

“We experience great things all day long that we fail to acknowledge,” Johnson says. “I don’t want to sound new wave-y, but 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. They’ve chosen to look at the good instead of the challenges.”

Years added? Maybe some, maybe none. "Even if I don't live a long time," Johnson says, "I'm happy with what I experience."