Your squat performance can be affected by poor mobility in your ankles and calves. Do this drill as part of your warm-up on leg days and you'll feel the difference.
Toe Touch Squat
In this drill, you'll use a forward bend initially to keep the abs and thigh muscles "quiet" and allow you to access a deep squat much easier.
The heel lift, which can be accomplished with a 45-pound plate, two-by-four, or something similar, will reduce the mobility restrictions within your ankles and calves. (If you can't touch your toes, you should work on that first with some leg lowering and toe touch drills.)
Once you're in the bottom position, with your butt nearly touching the backs of your calves, think about tilting your shoulder blades down and back. It's easy to have a rounded upper back when you first try this.
Make sure your elbows are inside your knees, with the arms straight. One of the great things about keeping the arms inside the legs is it will draw your chest up without forcing you into a ribs-flared position.
Just work on getting your body familiar with being in that deep of a position. Aim for 2-3 sets of 5-6 reps as part of a dynamic warm-up.