When done correctly and with proper focus, Pilates is not easy—no matter how fit you are. If you tried Pilates once or twice but weren't impressed, you probably weren't doing it correctly. And that's not your fault if your instructor (in class or on video) didn't explain it properly. When performing every single Pilates exercise you should also:
1. Breathe correctly. Joseph Pilates used to say, “Even if you follow no other instructions, learn to breathe correctly.” Use deep breathing (described above) to target and tone your deep transverse abs. Your inhale should expand the ribcage (diaphragm) but not the belly, which should be tight and flat as if you are wearing a corset. This helps you keep your core muscles engaged.
2. Concentrate on pulling your shoulders away from your ears and retracting your shoulder blades toward the center of your spine.
3. Properly align the spine. Your head and neck should follow the natural line of your spine at all times.
4. Focus on every movement as if it comes from the center of the body (your core).
5. Practice control. Don't use momentum to help you move. Movements should be done in a slow and controlled manner at all times.
6. Keep your body grounded and stable. If you're really focusing on the core, your body should be square on the mat and you should not rock or slide in any direction during exercises that involve lying, sitting, or kneeling. (This is one of the most common mistakes I see as an instructor.)
7. Work in an appropriate range of motion. Fitness enthusiasts tend to try the hardest options, even when they haven't truly mastered the basics with proper form. Similarly, wanting to work harder, many people will work in larger ranges of motion, but aren't able to stay grounded (point #6 above) when doing so. Only work to a level that allows you to maintain all of the points above.
The great thing about Pilates is that it offers something for everyone, no matter what your fitness level. If you started as a skeptic, consider revisiting Pilates by taking a class in your area or trying a fitness DVD. When you do, incorporate the points above and you will feel and see the difference. As Joseph Pilates himself said, "You will feel better in ten sessions, look better in twenty sessions, and have a completely new body in thirty sessions."