Wnder nobody mentioned goblet squats for improving squatting form. Those are easy to do, don't require too much equipement (heck, they can be done with BW with your elbows pushing your knees outward).
And I like them for "loosening up" the hips before heavy squat work. Less stress on knees due to the lack of heavy load, teaches you to push knees out, keep core tight, keep torso upright, etc etc... I think they are good for teaching the squat properly??