First off, let us recap the first two rules of movement:
Rule #1: Prioritize your spine.
This almost always takes the form of the bracing sequence. However, even for shapes and movements that demand global flexion or extension in the spine, the position still needs to be braced. If you cannot squeeze your butt and belly, you have gone into local flexion or extension. You have kinked the hose. This means that you can no longer stabilize your position on your own. If you cannot consciously squeeze it, you cannot use it.
Rule #2: Torque
Create rotation in your shoulders and hips. External rotation if your limbs are in flexion (in front of your body) and internal rotation if your limbs are in extension (behind your body). Creating torque gets your skeleton in a better position, and winds up your muscles to stabilize your skeleton in that better position, primarily in your shoulders and hips. This extra stability allows you to much more easily maintain a good position while are in motion.
These two rules can be done by themselves in a static position, which is where they can be taught first. But you have to learn to display these rules while moving, and especially while under stress. This is where the third rule comes into play.
ule #3: The one-joint rule
The one-joint rule states that the spine does not move while changing from one body shape to another. The rule of maintaining a neutral spine not only applies for static positions, but also, and more importantly, it apples for dynamic positions and movements while you are under stress (including exercising). This is the one-joint rule. When you are moving, your spine should be treated as one solid lever. There are no joints in your spine any longer once you have braced yourself.
After getting braced, I place one thumb on my sternum, and the other at my waist.
Understanding how to do this is more important than I can stress in text. Because it is movement of the spine under stress that creates most of the back pain people experience, developing some strength and proprioception (the ability to sense where and how your body is arranged in space) can save you from massive amounts of dread and unneeded medical payments.
The only places in your body where you should see large amounts of movements are in your shoulders and hips, and the joints outside of them. This also means that your shoulders and hips need to be able to move through their full range of motion (ROM) without pulling on and altering your spine.
Start with bracing yourself. Now with that braced position active, you need to be conscious of maintaining that position while you squat, lunge, deadlift, reach overhead, reach behind you, and while you carry weight, etc.. This takes practice. Unless you have been trained to move like this your whole life, it is going to be a new skill for you to learn. But as with any other skills and practices, once you train it consistently for a few weeks, it becomes automatic. Utilizing the one-joint rule, both in the gym and in your day-to-day life, will be a habit that will reward you for the rest of your life. Imagine never having to worry about dealing with low-back pain. Imagine never having to worry about developing sciatica or a shoulder impingement. Embody these concepts of taking care of your body, and they alone will drastically reduce your chances of many common ailments that plague so many people. And be sure to check out the video below for more visual cues about how to utilize the one-joint rule, as well as the previous two rules!