Why it’s a winner: Squats work multiple muscle groups — the quadriceps, hamstrings, and gluteals — at the same time. Also, they can be done pretty much anywhere. If you have a few minutes (even at your desk) you can always do bodyweight exercises.
How to: Keep your feet shoulder-width apart and your back straight. Bend your knees and lower your rear as if you were sitting down in a chair, keeping your knees over your ankles.
Practice with a real chair to master this move. First, sit all the way down in the chair and stand back up. Next, don’t sit all the way down; barely touch the chair’s seat before standing back up. Lastly, graduate to doing squats without a chair.
I often alternate between squats, push-ups and jumping jacks when I’m at work to get my heart rate and energy up. It’s a good mix of cardio with an upper and a lower body exercise that can be done anywhere anytime. I usually do 20 seconds of each with only a 5 second break in between for as many sets as I can in the time I have (usually only a couple of minutes in between tasks).