Stand with your legs shoulders width apart and your knees facing forward, also making sure your hips are square. The first action of a squat is hip flexion so initially stick your bum out slightly.
Slowly flex the hips and knees so you squat down till your thighs are nearly parallel to the floor and make sure your knees don’t go in front of your toes. Also keep your head facing forwards.
The KEY for performing good quality squats is to flex at the hips and do the action with CONTROL and SLOWLY on the way down. Also make sure you have even weight on your feet (not too much on your heels/toes).