I AM IN NO WAY AN EXPERT
but here is what I did when I had this problem…
I did bodyweight squats for like 2 weeks working on good slow form and really focusing on gettin into that position I wanted. I would stay down in the ATG for like 15 secs and come up. Slowly added weight on and within 6 weeks not only was I lower but my squat weight went up.
For a BB (Olympic squat), your legs should be about shoulder width apart with a SLIGHT turned out ward foot (not duck footed). Not everyone can go ATG, so if its hurting your knees stop, but ATG always helps
Stretches I just do basic hamstring stretches after 10 mins on treadmill to warm up. Nuttin fancy just like 5 mins or so. stuff like touch my toes and stretch to left and right. I also do a leg sweepin motion, hold onto the rack, stand on 1 foot, and sweep across in front of you with your other leg like a pendulem, then switch. Before I do a warmup squat set, I do 3-5 BW squats ATG and hold the ATG position for 15 secs or so
Make sure to train your hams too, not just your quads. As I got stronger, it was easier to go ATG cause my hammies were better do some RDLs and then see how you feel
Again, not an expert, not a coach, idk the physiology behind…just sayin what i did/do