Going down square on and off-centered behind the shot means the chest, and belly need to bend over the pelvis square on and off-centered as well. Getting the belly center around the belly button well positioned and comfortably bent flat over the pelvis is very important, this is where the body centers itself, breathes the chest, and powers the limbs. Not being too centered or off-centered behind the line of the shot is the solution to staying comfortable here. Almost all of the turn required should occur in the shoulders and arms, not in the torso and pelvis. Because of the squareness of the stance, some shoulder turn is necessary to tuck the right upper arm/elbow in line behind the head, but it must be gentle.
Side-on stance: Stand both legs and feet comfortably lengthwise behind the shot with whatever bend combination you find the most comfortable. Position the right foot somewhere outside the line of shot, angled out to the right. Stand the left foot straight ahead establishing good length difference between the feet. The width between the feet is considerably less than the width in a snooker stance, my left foot is only about 2 heels width outside the line of shot. The flatness of the torso in relation to the table is a matter of preference, you can choose to be as flat on the table as a snooker stance, or you can remain more elevated over the cue. Because the body is presented side-on, almost no shoulder turn is needed to tuck the right upper arm/elbow in line behind the head.
Once in a stance, the head, eyes, elbow, eye-of-grip, bridge, and cue, all need to be lined up together to deliver a smooth, relaxed stroke with the right forearm. The upper edge of the forearm should be presented facing the line of the shot over the cue, neither turned outward or inward. The right upper arm/elbow is significant, if it is not aligned, the upper edge of the forearm cannot be presented facing the line of shot, the eye-of-grip underneath cannot swing straight through, the head will want to move, and the stability of bridge and feet is compromised. The pendulum effect relies on a correctly aligned upper arm/elbow. If it is out of line gravity becomes your enemy rather than your friend and the muscles of the forearm tense to hold the cue in place as you stroke. Traditionally, the forefinger and thumb are the parts of the hand that grip the cue, but there are many variations that can work, it all depends on what feels right for your hand. Try the traditional single forefinger and thumb grip, two fingers and thumb grip, three fingers and thumb grip, middle fingers and thumb grip, and even a whole hand grip where all the fingers hold the cue. I recommend experimentation to find what suits you best. I use the traditional forefinger and thumb grip, and I find it works best by making sure that the forefinger is fully curled around the cue. That creates a necessary stability and makes it easier to release the other fingers, allowing them to touch but not grip. Where to grip the cue is different for everyone. Body height, arm length, and how flat you like to go down into the stance are all variables that effect where the grip should be positioned. Also, the grip position should change depending on the type of shot being played, so no particular grip position can be said to be correct for all situations. A simple technique for getting the grip position approximately correct for most shots is to position the grip two hand widths down from the balance point of the cue. The most common mistake people make is to not grip enough of the cue which tends to correspond with a stance too close to the shot and hunched up and crouched and leaned forward too much.
Step 2) [Head, Eyes] bows [Right Elbow, Eye-of-Grip, Bridge, Cue, Chest/Belly] over [Pelvis, Legs, and Feet] onto the {Line} behind the {Cue Ball}
Step 2 is the critical part of this drill. The important bit is the aiming of the shot from the head, as you bow down the elbow, bridge, and cue into place under the head. Once the elbow, bridge, and cue are in place, all the lining up behind the shot should be complete.
Bend the head down as straight as possible to keep a consistent view of the shot. As you go down onto the cue, pull back slightly with the right upper arm/elbow and eye-of-grip and extend gently with the bridge. This brings the cue up in against the chest, and helps line things up with the head. I liken this action to that of drawing a bow in reverse, one arm holds relatively still while the other extends forward. Both shoulders, arms, and hands need to move in unison for precision. It is important to get your weight slightly forward into the shot, with the pelvis slightly forward over the legs and feet. If your butt is sticking out over your heels, you are falling away from the shot and you will lack power in the stroke. Don't lean too far forward though, it is important that the pelvis, legs, and feet carry most of the weight, it is what this part of the body is designed to do. The heels and toes of the feet need to be firmly planted. On the table, the left arm should carry only some of the weight comfortably, creating the triangle or tripod of weight bearing points. The left arm should rest slightly bent on the table if it fits. In my experience, a completely straight left arm tends to exert unnecessary pulling pressure on the left chest part of the body. A too bent left arm, on the other hand, is likewise something to avoid because it encourages the body to hunch up and crouch and fall forward, instead of stretching comfortably out. A good tip is to make sure that the left shoulder/upper arm joint is as flat as possible to comfortably carry weight and stabilize the stance and minimize strain down the left side of the body. The bridge should be approximately one hand length away from the cue ball for most shots. You can vary the angle of the bridge hand, how much if at all is a matter of preference. The cue tip should be directly behind the cue ball at first, ready to move back with the first practice stroke. All of the bridge fingers need to be firm, although perhaps the forefinger needs to be especially firm since with the thumb it forms the base for the groove.
