I personally would start with breathing, bracing, and then breathing into that. For me that’s the hardest part.
Whenever I go to squat I do it like this.
1)Walk up to the bar.
2)Squeeze butt. Take a breath and get tight.
3)Pop under the bar while staying tight and getting into position. Breathe into the tightness to brace.
4)Now comes the second hardest part.At this point. The only thing in my mind is to get my knees out.
I do this by “screwing my feet into the ground”. What I learned before seeing k-starr explain this was to get my knees out. Before the lift and during the lift. The only way to do that is to externally rotate my thighs. It literally feels like i’m twisting my femurs.
It’s hard to describe. But if you plant your feet and screw your feet into the ground. Take note of what you are feeling in your hips. Now, plant your feet and replicate the feeling in your hips. What happens to me is my feet naturally screw into the ground.
I do this right before I unrack the bar, and then throughout the movement. I’m thinking of opening my hips/knees.
5) From there adjust everything else.
As far as going into overextenstion. I literally cannot overextend if I get myself to a neutral and then braced position.
So to recap. I personally would just practice bracing and breathing. Banded GM’s helped me a ton on keeping that tightness while moving.
P.s. Film yourself. This has been one of the most beneficial things I’ve done for myself. I literally watch every set after I do them on my cell phone. If I keep faulting to crappy form, I’ll drop the weight and try to find the weakness.