Finding it tough to motivate yourself? These strategies can help.

But once we find motivation, it doesn’t become a constant. It can come and go in waves.

“People tend to misjudge future levels of motivation — they don’t understand that high motivation today will drop down to low motivation or that other motivations will come in,” said B.J. Fogg, founder of the Behavior Design Lab at Stanford University and author of the book “Tiny Habits: The Small Changes That Change Everything.” “The other thing people get wrong is they think they’ll be able to sustain consistently high levels of motivation day after day. It’s just not how we’re wired.”

Another surprise: Motivation often comes from contemplating changing behavior, rather than before. Research shows that pre-motivational factors — such as risk perception and awareness of one’s own behavior — are important for people to build motivation to increase physical activity.

After we contemplate and mobilize ourselves to change our behavior, we often find that “it’s easier and more enjoyable to do than we thought it would be, and we find our rhythm,” said Wendy Grolnick, a professor of psychology at Clark University in Worcester, Mass., and co-author of the forthcoming book “Motivation Myth Busters: Science-Based Strategies to Boost Motivation in Yourself and Others.” “So instead of waiting for motivation to strike, it’s better to do something to spark it.”

With the right science-based strategies, you can make healthy changes, experts say.

Research suggests that self-determination theory — which refers to the quality, not the quantity, of motivation — matters most in changing behaviors. Ask yourself why you want to eat more healthfully, exercise more often, quit smoking or change other habits.

People feel most motivated when they have autonomy (when they feel it’s their choice to make this change, rather than feeling pushed or coerced), when they feel competent in making the change and when they feel connected to other people, Grolnick said: “When you see the value, meaning or usefulness to you in making the change, you’re more likely to sustain motivation.”

You can bolster your autonomy and competence with motivational interviewing, which helps you explore your personal reasons for making a habit change and what you’re willing to do to get there, said William R. Miller, a professor of psychology and psychiatry at the University of New Mexico and author of the book “On Second Thought: How Ambivalence Shapes Your Life.”

Consider the following questions:

• What are my three best reasons for doing this?
• How important is it to make this change?
• What steps have I taken to move in this direction?
• What am I willing to do to make this change?
• What am I going to do?

“Hearing yourself say it out loud can make it sink in as a commitment,” Miller said.

Announce your plans and ask for support from family and friends.

“The very act of asking for help is motivating because there’s some accountability in that,” Miller said.

Start with simple, bite-sized actions. To get into a regular walking routine, you could start by going for a walk around your backyard or put on your walking shoes, Fogg said.

“The starter step is kind of a mental jujitsu — it has a surprising impact for such a small move because the momentum it creates often propels you to the next steps with less friction,” Fogg said.

If you encounter self-control challenges, try a strategy called “temptation bundling,” Milkman said.

Temptation bundling lets you engage in a guilty pleasure only while you are doing an activity you want to make a habit. To exercise more often, read a page-turner or watch a certain TV show only while you are using a stationary bike or elliptical machine. To cook healthy meals, treat yourself to your favorite podcast or a beverage of choice while you are working in the kitchen. “It’s about making the path enjoyable,” Milkman said.

If you link a desired habit to something you already do (an anchor), you can create built-in prompts or reminders to engage in it, Fogg said. Some examples: After I get out of bed in the morning, I’ll do X number of push-ups or planks. When I see the stairs, I’ll take them instead of the elevator.

By letting one action become the trigger for another, the new behavior becomes automatic, Grolnick said.

Surround yourself with people who have the habits you’re trying to cultivate. “By watching people around you, their good habits will become normal to you, and their influence will rub off on you effortlessly,” Milkman said.

Ask someone with a stellar diet how they manage to eat healthfully at restaurants or inquire how a busy colleague always finds time for exercise when traveling for work. Once they share their secrets, “copy and paste” them into your life, Milkman said.

“A lot of people think there’s some magic number of days to make a new behavior a habit,” Milkman said. But depending on the person and the activity, there are huge variations in that timetable.

In a pair of studies, Milkman and her colleagues examined habit formation among people who aspired to go to the gym regularly and hospital workers striving for better hand hygiene. The researchers found that while it typically takes months for people to become regular gym-goers, better hand-washing in the hospital becomes automatic in a matter of weeks. Milkman said: “It takes a meaningful amount of time to change habits,” often longer than people think.