Personal trainer Joel Harper has spent two decades helping his clients (from Olympic medalists to Dr. Oz) reach their fitness goals, and over the course of his career he’s discovered the reason why some people thrive and others fail: It’s all about attitude, he argues in his new book, Mind Your Body: 4 Weeks to a Leaner, Healthier Life.

Harper has taken years of experience and distilled it into "10 core concepts for optimal success." Health spoke with Harper about these rules, and how to put them into practice.

Shut out the noise
By “noise,” Harper means the constant stream of negative thoughts that runs through most people’s minds. That mental static is your biggest obstacle, he says; learning to filter it by focusing on positive thinking is essential to your success.

Maximize inner motivation
To do this you need to be absolutely clear about why you want to get fit. “Figure out what’s really important to you,” Harper urges. “Do you want to lower your blood pressure? Fit into a size two? Or do you just want to feel better?” Motivation that lasts can’t come from an outside source—like your doctor or a loved one who wants you to slim down. It has to come from a personal, deep-rooted desire for change.

Cultivate grit
Grit is the resolve and passion required on a daily basis to pursue a long-term goal. To cultivate grit, you have to commit to consistency no matter what. A fit person wakes up every day knowing she will do whatever it takes to stay on track—whether that means getting up an hour earlier to make it to the gym before work or squeezing in a power walk at lunch. The secret is focusing on the thoughts that drive and inspire you. If it helps to remind yourself how good you’ll feel post workout, for example, do that. If it motivates you to daydream about your future toned tummy, do that. Concentrate on exactly what you want to achieve and make every day count.

Set specific intentions
The more detailed your daily goals and plans, the better. In his book, Harper cites an English study on women enrolled in a weight loss program: The researchers asked about half of their subjects to write down their strategies for managing temptation (for example, When sugar cravings strike, I will make a cup of tea). After two months, those women had lost twice as much weight as women in a control group.

Visualize success
Harper has all of his new clients close their eyes and imagine their ideal body—both what it looks like from head to toe, and how it makes them feel. Then he tells them to go shopping: “I say to people, ‘Hey if you want that body, then buy clothes that would fit if you had it. And try them on every day until they fit.’”

Eliminate excessive choices
Chocolate croissant or steel cut oats? Grilled salmon or a quesadilla? When you have to make these types of dietary decisions all day long, you may end up exhausting your willpower. Planning your meals in advance, however—even just one meal per day—can make it easier (and less stressful) to eat healthy.

There are a few classics, like “If I don’t exercise at lunchtime, I’ll do it tonight” or “I’ll have ice cream today and get my diet back on track tomorrow.” But any sort of procrastination runs the risk of bumping you off course, Harper says. His advice: Don’t give yourself an out, and stick to the path that leads to your goal.

Yield to traffic
It’s inevitable that from time to time your healthy routine will get interrupted by forces outside your control, like when your partner proposes an impromptu date night right after you’ve bought salad ingredients. When that happens, try to go with the flow and enjoy yourself.

Believe it and become it
This rule is simple: “If you believe you can be in amazing shape, then you’ll do things on a day-to-day basis to accomplish it,” says Harper. The problem is, many of us carry around defeating beliefs. When you recognize a negative thought (like, “I’m so uncoordinated”), ask yourself why you think that way. You may discover the criticism originally came from your parents, or your sibling, or a childhood buddy. “Don’t give those outdated internal beliefs power,” Harper says. “Just let them float away, like leaves that have fallen into a river.” You have control over your thoughts, he insists; they don’t have control over you.

Jump for joy
Harper’s most successful clients are the ones that celebrate their milestones. If you don’t appreciate your successes along the way, “you risk becoming emotionally numb, nonreactive,” he explains. But giving yourself regular (healthy!) rewards (like a massage, for example), provides a little “added oomph” to keep going and push yourself even harder in the long run.

-