The body weight squat is arguably the single best exercise you can perform for lower body strength.  It is a very versatile exercise.

To perform the body weight squat:

1. Stand with your feet shoulder width apart with your toes slightly turned out.
2. Extend your arms out in front of you at shoulder height, parallel to the ground.  Your arms will act as a counter balance and help you maintain good form through the entire range of motion.
3. Start by rocking your pelvis forward and sticking your buttocks out to stabilize your low back by engaging your low back muscles.
4. Slowly bend your knees and lower your body in a controlled manner until the top of your thighs are parallel to the ground or you feel like your heels are going to leave the ground.
5. Pause at the bottom of the squat before pushing your heels into the ground and returning to the starting upright position.

Attempt 10-15 repetitions per set.  Perform additional sets as your strength increases.  Each repetition should take no less than 5 seconds (2 seconds down, 1 second pause, 2 seconds up).  As always, listen to your body.

Variations

One of the great things about the body weight squat is that you can vary the exercise to make it more intense as your strength increases or to target the exercise to specific muscles or activities.

• If you want to develop explosive strength in your lower body, add a bit of plyometrics to the squat.  For instance, instead of returning slow to the standing position from the bottom of the squat, explosively leap out of the squat leaving the ground and softly landing on the balls of your feet.  Some people refer to this variation as a jump squat because you are effectively jumping from the squatting position.
• If you wish to develop further leg strength, balance, and core stability, perform a one-legged, body weight squat.  Perform the same squat above except extend one leg in front of your body.  Use a chair or other stable object during this exercise until your balance improves.
• If you wish to target your lower leg muscles, perform the squat as described above but extend up onto your toes at the end of the squat and hold for a count of 3.  This takes balance so be careful.