To truly change your body and your weight, you need to have the right mind-set. Take a few minutes to consider the following before you even start this plan.

Be honest about your motivation
"More people come to me looking to save their wardrobe rather than their life," says Stephen Gullo, Ph.D., author of The Thin Commandments Diet. So if fitting into a smaller size is what's driving you, embrace it! Hang a picture of the outfit you hope to wear someplace you can see it. If lowering your disease risk and adding years to your life is your goal, post shots of family and friends on your fridge as a reminder of what you're working so hard for.

Deal with distractions
Do you have the emotional resources to take on this challenge right now? If you're coping with a heavy workload or a difficult relationship, you might focus on maintaining your weight until the other issues resolve, says Anne M. Fletcher, R.D., author of Thin for Life. But there are exceptions: Sometimes people slim down in the midst of chaos because weight is the one thing they can control. Whatever you decide, this 21-day plan can help.

Take the mood out of your meals
If you're prone to emotional eating—and most of us are—come up with a non-food outlet (taking a walk, calling a friend) to help you cope with stress.

Benefit from your mistakes
Look at what you've done before to lose weight or get fitter—and vow to do better. Did you plan to hit the gym at 5 a.m. every day and then find yourself hitting the snooze button instead? Unless something has changed, failed strategies won't work this time around either.

Pick a start date
Choose a typical day to initiate this 21-day program—not one when you have to take a business trip or go to a party, for instance. Prepare by making time to buy the groceries you'll need and finding child care during workouts.

Pick up Shape's special Make Over Your Body issue for complete details about this 21-day plan. On newsstands now!