squat

Squats are also highly versatile: you can do them anywhere — even while brushing your teeth. Multitask by adding bicep curls and other moves to make them harder.

Here's a primer on how exactly to do the perfect squat.

Stand with your head facing forward and your chest held up and out.
Place your feet shoulder-width apart or slightly wider. Extend your hands straight out in front of you to help keep your balance. You can also bend the elbows or clasp the fingers.
Sit back and down like you're sitting into an imaginary chair. Keep your head facing forward as your upper body bends forward a bit. Rather than allowing your back to round, let your lower back arch slightly as you descend.
Lower down so your thighs are as parallel to the floor as possible, with your knees over your ankles. Press your weight back into your heels.
Keep your body tight, and push through your heels to bring yourself back to the starting position.
Start with three sets of 10 squats, and then add more reps (12, 15) as you get used to the motion. It's definitely awkward at first, so don't expect to master the squat right away. Focus on your form, and then worry about adding reps.