Squat

Set the barbell in a rack just below shoulder height. Step under it and place the bar evenly across your upper back (on your traps), not on your neck.
Grip the bar securely, lift it from the rack, and take two or three small steps back. Stand with your feet shoulder-width apart, toes pointing slightly out.
Take a deep breath to brace your core. Keep your chest up, your back straight, and your gaze forward.
Initiate the movement by pushing your hips back and bending your knees simultaneously. Lower yourself until your thighs are parallel to the floor.
Drive through your heels to push yourself back up to the starting position, squeezing your glutes at the top.

Tips

Before you descend, take a deep breath into your belly and brace your midsection outward in all directions, as if you were about to absorb a punch, and hold that tension throughout the rep.
Push your knees outward in the same direction as your toes as you lower and rise, keeping them tracking over your feet rather than caving inward.
Keep your chest up and your torso as upright as your mobility allows by actively pulling your elbows down and back under the bar throughout the movement.

The heels rise off the floor during the descent, shifting the base of support forward and disrupting balance.
The knees collapse inward as you lower or drive back up, rather than staying aligned over the toes.
The torso pitches sharply forward at the bottom of the squat because the upper back rounds and the chest drops toward the thighs.