Grant, please don't be "one of them people" who pile on the weight and only do partial reps. It is not only dangerous, it is also a waste of time, and you'll be the guy in the gym that everybody laughs about. The correct way of performing a squat is to go down to parallel... As with any exercise, a complete range of motion is key. Decrease the weight that you're using if necessary and use good form; head up, back straight, etc. and do full squats.