I found this book by Danny John called From the Ground Up which has the best plain English guide for good form for squatting with a barbell which I have ever read. My trainer just says to keep the weight over your heels, but never exactly how do that. The tips in this book were obviously written by a coach who has taught a lot of kids how to lift. For example, to correct your stance, jump up and down three times. Where your feet land on jump 2 or 3 is the proper natural foot alignment for a squat. Who knew? If there's a question about what he means by "chest up", he says "imagine being on a beach when a bikini model walks by", which is an arched back, lats wide, chest up posture, he just calls it "Muscle Beach chest" from that point forward. I've always been impressed in my experience with hockey coaches by their practice of associating complex concepts with two or three word commands which can be barked at game speed to correct an athlete. I know that "soft hands!" echoes in my head every time a pass bounces off my stick, or "hockey position!!" if I catch myself standing straight legged in skates and can't stop or turn quickly enough. After reading that, I imagined him shouting "Muscle Beach" across a stinky gym at some young chump who is lifting incorrectly. Going down, you imagine your feet are stuck to the ceiling and you have to pull your butt to the ceiling. Then "push the floor away" to get the bar going up. That makes so much more sense to me than "stay on your heels."