Lose weight. Quit smoking. Spend less time online. Whatever you resolve to change this New Year’s Day, psychologists say you need a plan — not just a resolution.

Resolutions are never a waste of time, insists John Norcross, a psychology professor at Scranton University and author of “Changeology: 5 Steps to Realizing your Goals and Resolutions.”

Norcross has tracked and studied resolutions for over 30 years. He says successful resolvers improve themselves in major ways and often add years to their lives.

But real change takes work. According to Norcross’ research, it takes about three months for a change to become routine. After six months, about 40 percent of people will stick to their resolutions, he says.

If you make it to then, he says, you’re likely to maintain your resolution for life — but you need an actionable plan to get there.

Here’s how experts say you can make your resolution stick through 2019 and beyond.

Be realistic and plan ahead

Successful resolvers begin planning their goals at least a week before Jan. 1, says Norcross.

“They are the people who are planning for a resolution — not just wishing at 12:01 a.m.,” Norcross tells NBC NEWS BETTER.

They also focus on how they will achieve their resolutions.

“A resolution isn’t a wish, it’s not a dream,” Norcross says. “It’s identifiable behavior that you can work on.”

Example: Instead of resolving to lose 60 pounds in a year, resolve to lose a few pounds a month, and create a consistent plan on how to do it.

Tip: Record and track your progress. Self-monitoring increases your chances of success.

Use your brain’s ancient reward system

A resolution is a lot more than just getting rid of a bad habit, according to Elliot Berkman, director of the University of Oregon’s social and affective neuroscience lab.

To undo a bad habit, he says, you’ll need to replace it with a good one.

“Habits are basically behaviors that become entrenched because of our very evolutionarily ancient reward learning system,” Berkman explains.

Habits are usually a good thing, he says. Without them, you wouldn’t be able to drive a car — a task that requires you to do many things at once without thinking.

A habit forms when a certain behavior is consistently rewarded, explains Berkman. The first time you turned the steering wheel of a car and it went the direction you wanted, it triggered your brain’s reward system. Over time, driving became habitual, Berkman explains.

But the same system also rewards negative habits, he says. “When I’m feeling tense and I have a cigarette and I feel less tense, that’s also rewarding,” he says. “That also gets embedded by the very same system.”

Your resolution should focus on using this same reward system to form the new habit, he says.

“You come up with a new behavior that will also be rewarded,” he says, “and over time, you replace the old habit with a new habit.”

Example: If you resolve to stop smoking, replace your cravings with a different fix — like chewing gum, or exercising.

Tip: Reinforce progress at certain milestones with healthy rewards. A resolver trying to lose weight, for example, can treat himself to a healthy snack for every five pounds he loses.

Eliminate triggers from your environment

When it comes to making successful resolutions, our environment plays a major role. Cues that can trigger your bad habit should be removed from your home, says Berkman.

Certain rituals can also trigger negative habits — like smoking after a meal, or looking at social media before bed. You’ll need to replace those rituals with positive ones, he adds.

“Identify the times and places and situations where you’re likely to smoke, and then come up with a plan ahead of time to address it,” he says.

Examples: If you resolve to quit smoking, eliminate ash trays from your home, which can trigger cravings. If you typically smoke after dinner, plan to have gum instead. If you are trying to lose weight, throw away any unhealthy snacks in your kitchen.

Rearrange your environment

Next, you’ll need to rearrange your environment to reinforce the good habit you’re trying to create, says Berkman.

Examples: If you are resolving to exercise more, put your gym bag in front of you door to remind yourself to go to the gym before work in the morning. If you want to reduce screen time before bed, keep a good book on your nightstand. If you’re resolving to eat better, stack your fridge and cupboards with healthy snacks.

Get social support

Family, friends, and coworkers can be major triggers for bad habits, according to Berkman. If there are people in your life who share your bad habit, he says, ask them to make the resolution with you.

“You’re going to need social support,” he says. “Sometimes it’s easier to change together, with your partner, with your family, with your friends.”

But not everyone is willing to change. You may need to consider reducing the amount of time you spend around certain people if their behavior is going to trigger your bad habits, says Berkman.

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