The lifter must determine how they will setup and what "type" of squat they will perform, you have bar position, stance, flexibility, etc to take into consideration. From there watch successful lifters squat and pay very close attention to how they perform the lift - positions, timing, etc. Record your squats to see what your doing and what needs to be done. Seek advice from those who know what they're talking about and knows how to perform the lifts not someone with a big mouth and nothing to back his words up (look at his own lifts or people they have coached).
Specifics are often determined by the lifter's body and the style of squat they choose to perform but the few things that apply to all:
1 - Chest must remain high with the shoulder blades pulled back and very tight.
2 - Fill stomach with air and brace the abs hard for the entire lift.
3 - The lift always begins by pushing the hips back, first. Not bending at the knees.
4 - On the descent, actively push the knees out to the side so that they track over your feet which are angled slightly outward.
5 - On the descent and ascent, keep the weight over your mid-foot or your heels. Do not let the weight shift to the forefront.
On depth... this is something determined by the style of squat, flexibility, and purpose of the squat. Olympic lifters want to attempt to reach rock bottom whereas powerlifters may only prefer to focus on reaching at least parallel. For rec lifters, it doesn't matter as much as long as the squat reaches parallel, which is the point where the crease of the hips is inline with the top of the knees.
Squatting deep is no more "dangerous" than squatting to parallel as long as the lower back remains tight and flat. For the "lifter" in the original post the 5 suggestions above should help keep the back flat while getting low enough, should he wish to continue to squat deep. If it does not, the issue may be flexibility in the ankle joints in which getting a pair of olympic weightlifting shoes or increasing ankle flexibility through stretches can eliminate the issue. If neither are viable options, the lifter should only squat down to parallel or the lowest point in which he/she can maintain a rigid back. And as always, never sacrifice form over weight when LEARNING a movement.
Last edited by Pull14; 02-21-2012 at 05:07 PM.