Have a box placed behind you in the squat rack. To test proper height, when you sit on the box, your thighs should be at or slightly above parallel to the floor.
Be in a strong athletic position: knees flexed, core and glutes activated, chest up, and shoulders back.
Get underneath the bar, placing it on your traps
Have your hands outside shoulder-width in a position where you can create torque in your shoulders. You want to keep your shoulders pinned back. The equates to a strong upper back position.
The bar does not sit loosely on your back. Arms lock the bar into your body.
Imagine pulling your elbows under the bar with your chest
You want your torso in a strong, vertical position.
Your chest is up and eyes fixed straight ahead.
Unrack the bar and step back one foot at a time.
Be aware of the box positioned behind you.
Place your feet slightly wider than a normal squat. Toes pointed out slightly as well.
Push your knees out and 'screw' your feet into the floor. Brace your core again.
Push your hips back and sit softly down & back into the box.
The box allows you to sit back more in the squat equating to more hamstring and glute activation.
Sit back into the box. Your upper box goes back with your lower half.
Your upper body is still locked in and tight.
Don't tap the box with your glutes then stand up.
Using your glutes and hamstrings, stand up into the starting position.
Squeeze your glutes at the top.
*Tips*
Sit softly on the box while maintaining your core strength. Don't collapse on it, this will cause havoc on your back.
Perform with light weight and grove the proper bar path. Going heavy without proper knowledge of technique can be dangerous.
Don't overextend/arch your back. Focus on core tightness and a neutral spine.