Step into the squat rack and adjust the pins so that you can easily un-rack the bar. You should also make sure that the safety catches are in place in case you reach failure and can't lift the weight out of the bottom position. Space your feet slightly wider than shoulder-width apart with your toes pointing slightly outward and rest the bar on your lower traps and rear shoulders. Grip the bar with your hands spaced evenly apart and clear the bar off of the pins. Keeping your head up and abs tight, take a step back. Make sure that you are in a secure position with the bar balanced and with a solid base. Start the movement by bending at the knees and squatting down toward the floor. As you squat down make sure that your head is up, your abs are tight and your lower back is arched. Continue to descend until your thighs are at least parallel to the ground. Once you reach the bottom, drive the weight back up until you are in a standing position. Continue until you have completed your desired number of reps and then re-rack the bar.
Tips: Squats are a big power movement and it is important that you use good form at all times. If you get sloppy by using momentum or twisting and jerking around you will be at high risk for an injury. Make sure that your abs are tight at all times and that your head is up. Your lower back should also be arched throughout the exercise rather than rounded out. When you reach the standing position, don't lock your knees out as this will stress the joints. I wouldn't recommend taking this exercise to all-out failure since you could easily hurt yourself. You should simply continue the exercise until you are one rep short of failure and then re-rack the bar. You should start out by using very light weights until you get a good feel for the lift and can execute it with perfect form.