There were quite a few posts on full squatting recently, so search for them. Also, there is a current post somewhere with videos of OLers squatting, where you can see what ideal form looks like. Mike Robertson's articles are golden, there are two of them dealing esp. with squat.
Be aware that powerlifting (PL) and athletic/olympic full squat are actually two completely different exericses. Some people, like C. Thibaudeau or Glenn Pendlay, think that unless you're competing in PL, you should mainly stick to full squats.
Some of the differences are:
In OL squat, you squat down, between your legs. Your shins will probably come over your toes. In PL squat, you squat sit back, trying to keep your shins perpendicular to the ground.
In OL squat, you keep your head in neutral position, looking straight in front of you on ascent. In PL squat, many competitiors look up at the ceiling.
In OL squat, you use a narrow grip on the bar, somewhat wider than shoulder width. In PL squat, you use a much wider grip, almost to the end of the bar.
And of course, in OL squats you go all the way down. In PL squats, you go somewhere like 55-70% down, depending on your leverages.