Maintain a slight knee bend and tight core with a braced neutral spine. You do not want an overly arched back.
To actively brace your core:
Keep your rib cage over your pelivs.
Activate your glutes by "screwing" your feet into the floor.
Shoulders are pulled back.
Eyes fixed straight ahead, neck in a neutral position.
Set the barbell across your lower traps. Keep your chest up and shoulders pinned back.
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.
Imagine pulling your elbows under the bar with your chest up and shoulders back.
The bar is not sitting loosely on your back
Unrack the bar and step out of the rack/stand.
Feet are just at or just outside shoulder width.
Take a deep breath and fill your stomach with air to create more core stability.
Initiate the movement byhingingforward at the hips while maintaining a strong core and knee flex. You want to maintain a neutral back & neck.
You will continue to lower yourself down until you cannot maintain a neutral spine.
Another reason to practice with the bar first, to find your end range-of-motion.
YOU ARE NOT ARCHING YOUR BACK TO SUPPORT THE BAR.
Engage the hamstrings and glutes to reverse the movement. Keep your core braced and knees slightly flexed.
Your upper back tightness is CRUCIAL.
*Tips*
Begin with just the bar before adding on weight to practice and fully understand the motion.
NEVER overload this exercise, there is a high injury risk with this movement if performed incorrectly.
Program this exercise as an accessory movement or within your warmup to activate your posterior chain.