The overhead squat is a great tool for exposing and overcoming imbalances in your body. Inflexibility and weakness in the lower back, abdominals, hips, glutes, and shoulders, will be exposed and with practice/work can be improved.
Use shoulder dislocates to warm up shoulders. Begin the overhead squat with light or no weight. Your depth and balance will improve as you practice and increase flexibility. Overhead squats are tremendous for increased trunk strength and will improve your back squat.