10. Don't skip stretching.
Stretching keeps your muscles flexible, helping to prepare them for exercise and recover from the effort afterward. Skip the stretches, and you won't get nearly the benefits you should from aerobic exercise and resistance training. (Get started with these 3 feel-good stretches .) "Stretching helps you move freely during aerobic exercise, it enables your muscles to build more strength during weight training, and it helps keep muscles long and lean," says Sharon Willett, a physical therapist and sports trainer at the Virginia Sportsmedicine Institute in Arlington, Virginia.