This is the highest point of a squat. Your knees should not be locked and you should not be standing straight up. The bar should rest across your rear deltoids (back of the shoulders) or your trapezius muscle below the neck. Make sure you squeeze your shoulder blades and trapezius together as tight as possible when supporting the bar. Make sure to try and raise your elbows and pull the bar down into your body.
Keep your chest up and proud. Create a natural curve with your back, pick a point to look at directly in front of you and never take your eyes off of that point through out the movement.
Tilt forward at the hips and take a wide stance with your legs. Make sure your feet are slightly turned outwards. You should feel very tight and contracted, yet comfortable standing.
The descent starts from the hips. As you begin to lower yourself closer to the ground you should be pushing your hips backwards not downwards. As your body begins folding into itself you must keep your back arched and your chest raised high.
One key factor in squatting is the knees. It is not safe to have them drift past the front of the feet in the initial descending phase. The closer you keep your knees aligned with the center of your feet the better. You should be lowering yourself slowly and controlled while listening for any snap, crackle or popping sounds from the knee. Do not buckle your knees inwards or outwards. They should be following the direction of your toes.
You will know when perfect technique is executed when there is silence from the joints and pressure on the muscles of the leg not the knee.
Slight drifting of the knees past the feet may or may not occur. It is ideal to focus on your hips being pushed back as far possible. Keep your weight focused on the heels and have a solid arch in your back. Your eyes should be focused on a point in space you chose earlier in the stance position. Your knees should not be buckled inwards or outwards they should be following inline with your toes.
You will know you are in the correct ending position when there is pressure on the lower back and leg muscles, not the knee joint, you are staring up at a designated point in space and your chest is turned upwards thus creating a natural curve in the back.