One thing I noticed is that I would recommend keeping your head up and fixed on a visual target in front of you. Notice how with each rep you look down.
This forward flexion of your upper torso will cause you to lose the strength in the traps and erectors in the upper thoracics. By looking down, you are putting yourself in a weaker position and splitting forces.
Or pick a spot on the floor about 6ft in front of you and stare at it intently. Try to keep your chin tucked and follow the spot with your eyes, not your head.
Proper neck position facilitates hip drive; it has been my experience that if you pick a spot not on the floor, your neck will go into extension at the bottom of the squat, and you will try to ‘good morning’ the weight up as you start to struggle.
Definitely never look down or to the side with a bar on your back.
Also, try to het your hips forward at the top before executing the next rep.[/quote]
Yes. Squeeze your glutes at the top of each rep, otherwise the rep isn’t complete. This has made a huge difference for me.
You may want to buy a book called “Starting Strength” by Mark Rippetoe, it is an excellent reference for form on the big three, as well as the press, power clean, and some assistance exercises. I learn something new every time I read it.