The overhead squat is a movement that we see fairly often especially with its involvement in other exercises such as the snatch, so its important that we work the movement and try to refine our technique so we can get stronger and more stable in that overhead position. Mobility plays a huge role in the technique proficiency of this movement, so if your mobility is the reason you struggle, it is important to address that first.However, there are a few faults i see on a daily basis that need to be fixed. The main issue is having a soft overhead position, and not keeping and upright torso, or bending forward at the waist. To correct this, we will lift the chest, and externally rotate the armpits while pressing up on the bar through the shoulders and upper back, to find a better overheard position. The better our overhead position can be the more efficient we can be in all of the movements involving overhead squats. Here is a great video from CrossFit HQ on some overhead squats, i really want you to notice the posture, and overhead position of these athletes and try to apply that to your own training.
Exercise: Overhead Pause squats 6x2 (pause at the deepest part of your squat for a 3 second count before standing up)