Barbell squats:
Approach the barbell located at your collarbones level and grab it just outside shoulder width. Slightly bend your knees and step forward. If you do everything right, the bar will lie on the trapezoidal muscle and be supported by the posterior deltas. If you feel uncomfortable, step away and try to approach to the bar again.
Step under the barbell and rest it on your back. Lift the bar off the rack by pushing up with the legs and take a step back from the rack. Set your feet shoulder-width apart, bend at the knees slightly, pull in your lower abs, and set your head in line with your spine, keeping eyes forward.
Once positioned correctly begin the squat by bending at the knees and hips together to lower your body. Keep your heels flat on the floor.
Strongly push yourself back up to the starting position mirroring the descent.
Mistakes and Recommendations:
Barbell position. If you lower the bar below the rear deltoids, the buttocks will work more. Such a position is not recommended, since the risk of balance loss increases.
Squat depth affects the buttocks involvement. A lower squat increases the movement amplitude, which positively affects its efficiency. If your goal is muscle gain - fall just below the horizontal position of the hips. If you are a weightlifter, squat to the end.
Knee position. One of the main rules of a safe squat: knee joints should not go beyond the socks. If it happens – try to work on your technique!
Choose the feet position based on your individual properties. Make sure that the socks are in the same direction as the knees.
Mistakes: back rounding, no lower back arching, bringing the knees inside, heels raising, back work (drive through your heels!).

Barbell squats.