1. Get a professional assessment. "No serious athlete would ever begin a new training program without an evaluation -- neither should you," says Denver sports psychologist Mark Mobley. Schedule an appointment with a personal trainer who can evaluate your cardiovascular, strength, and flexibility levels. These tests will establish a baseline to measure your progress against.

2. Set attainable goals. "Saying you want to be in excellent shape by spring is both vague and unrealistic," says Amanda Vogel, M.A., executive director of group exercise at FitCity for Women in Richmond, British Columbia. "Ask yourself what getting 'in shape' means. Then narrow it down." Focus on small goals, such as making it through a step aerobics class, to achieve bigger aims, like losing weight.

3. Make time. Lack of time is one of the oldest excuses for giving up a fitness program. Establish a consistent block of time for exercise, and avoid an all-or-nothing attitude. If time is tight, settle for less. "Squeeze in a quick 30-minute workout if that's all the time you have," Vogel says.

4. If at first you don't succeed . . . Don't like your gym? Switch to one that's more inviting. Birthday-cake blowout? Wipe the crumbs off your face, and plan your next healthful meal.

5. Be accountable. You're less likely to skip a workout if someone is waiting for you to show up, so find a workout buddy. And don't be afraid to spread the word about your fitness resolutions. The more people who know (and keep asking about your progress), the harder it will be to quit.