By: Al Duncan
There are many good books on learning Taijiquan such as "The Principles of Tai Chi" by Paul Brecher.
One classic reference is Yang Cheng-Fu's "10 Important Points". Here is another translation of the 10 Essential Points.
A valuable reference is "Acupuncture Points Related to Chen Taijiquan" provided by Yan Gao-Fei. This document can be found on the Pennsylvania Chen Taijiquan Association website. This information applies to all styles of Taijiquan.
Although some of these references can be applied by the beginner to his Taijiquan, many are more advanced concepts. There are a whole series of concepts that should be practiced and incorporated into your Taijiquan no matter what level you are at. Here are some I can think of:
1. The Feet
The bottoms of the feet must be kept flat on the floor; that is, the weight should be spread evenly over the entire bottom of the foot. The sides of the feet should not lift up even slightly as the weight is shifted from side-to-side. Likewise, the toes or heel should not lift as the weight is shifted forward and backward. The muscles in the ankles must remain relaxed in order for the feet to stay "nailed" to the floor. Don't tense the muscles of the foot. Try to keep your weight spread evenly over the entire bottom of the feet while doing the form.
The feet must be positioned a shoulder width apart (since the North American body shape is often shoulders wider than hips, some students may find positioning the feet a hip width apart more comfortable). When measuring the distance between two joints (such as hips or shoulders) use the distance from the center of the joints. Note that the "shoulder width apart" also applies to the width of stances such as "Brush Knee" and "Grasp Bird's Tail". The minimum length is to have the heel of the front foot in front of the tip of the toe of the rear foot.
2. The Knees
Don't let the knee extend beyond the end of the toe to avoid muscle strain. Don't let the knees move from side-to-side in movements such as "Wave Hands". In all stepping and movements in the form, keep the knee in line with the foot - don't let the knee move left or right of a line from the hip to the foot.
3. The Hips
One of the most important parts of the body when doing the Taijiquan form. We non-Orientals don't keep using our hip joints as a ball-and-socket joint throughout our lives. We tend to begin to use them as "hinge joints" instead.
Here is a good way to test the condition of your (or someone else's) hip joints, its called "rolling on the wall". Relax your back and hips against a wall with the knees slightly bent (feet shoulder width apart). Have someone hold your knees so they cannot move from side-to-side, and keeping the shoulders properly over the hips (no twisting), roll from side-to-side on the wall. If you have loosened up your hip joints, you will find this easy, the knees will only move forward and backward and will not move from side to side. If you have "hinge joints" for hips you will find that you can't even move - I know because this is how I was when I started learning Taijiquan.
It is extremely important to loosen up your hips right from the start of your study of Taijiquan. Trying to do the form with movements like "Wave Hands" when you have "hinge joint hips" will cause you to twist at the knees and ankles - resulting in soreness in the knees/ankles at the least and injury at the worst. There is also the requirement in the form to be able to open the legs (open the hips) to angles greater than 90 degrees while keeping the knees on the line from the hip to the foot.
In addition to learning to keep the muscles in the weighted hip from tensing up, you must also learn to relax the un-weighted hip muscles. If you accomplish this properly, the bottom of the un-weighted foot will feel suddenly attached to the floor. Moving from the weighted leg to the un-weighted leg will feel like you are sliding across from one to the other.
4. The Lower Back
This is another important part of the body when doing Taijiquan. Here is another simple test to check your lower back called "leaning on the wall". Relax your back and hips against a wall as you did in "rolling on the wall" and see if you can stick your fingers between your lower back and the wall. If you find a large gap there, it may be caused by an excessive "S-curve" of the lower spine. One way to help fix this is to spend quite a bit of time "leaning on the wall" while trying to straighten out the lower back. If this is uncomfortable, you may have to try laying on your back for extended periods on a carpeted floor with the feet up on a couch (knees at right angles) and let gravity help straighten your back.
There have been several discussions on the S-curve of the spine, and whether trying to straighten the lower back is "normal". Personally I find that inventing chairs to fit our society of "S-curved spines" to be not normal - why not work on straightening our backs?
In Taijiquan, the lower back must be straightened to help drop the tailbone in order to establish the connection or straight line from the top of the head to the ground. The expression often used is to "tuck the tailbone under", this expression is how it feels to straighten the tailbone so it is aiming straight down instead of pointing slightly to the rear (caused by the spine S-curve).
Proper relaxing (opening) of the lower back (in addition to relaxing the hip joints), will result in a feeling of ones weight "dropping" into the feet. As you can see, relaxing the lower back is connected to relaxing the hips.
5. The Torso
Keep the stomach muscles relaxed (empty) at all times. Relax the chest (empty the chest) so that it feels like the muscles on the outside of the rib cage are "dropped". You must learn to let the muscles of the chest and back relax so that you get the feeling that all the muscles seem to be "sliding down" or hanging from the rib cage.
6. The Shoulders, Arms and Hands
You have to learn to be able to get the shoulders to naturally "hang down" without having to force them down. This can be very hard to do if the muscles tend to be tense or shortened due to not keeping them stretched out. One technique to help stretch out these muscles which helped me, is to stand with arms hanging at your sides while holding weights in both hands. These can be the type which fasten around the wrist or other small weight which doesn't take much effort to hold in your hand, since gripping something can also cause the muscles of the arm to tense. While standing with these weights, focus on relaxing the elbows, shoulders and all muscles in the arms.
Perform the opening movement of the form repeatedly (very slowly) while focusing on where tension is occurring in the muscles of the shoulders/arms. Try to isolate and relax these tense muscles so that raising and lowering the arms becomes more effortless. Note though that raising and "supporting" the arms while raised won't become effortless until you can achieve all the "basic" points.
Keep the hands relaxed but the fingers are kept gently straightened, don't let the fingers curl. The hands are kept in line with the forearm, never allow the wrist to bend more than about 30 degrees.
7. The Neck and Head
Keep the chin pulled back to help straighten the neck, but at the same time try to remove any tension from the neck muscles. Don't allow the head to tilt in any direction - don't look down at your feet.
8. The Whole Body
Practice doing the form very slowly so that every time you shift your weight to one leg, you can take the time to let the body settle on the hip and look for the establishment of the "straight line" from the ground to the top of the shoulder/head. Also take the time to "review" all the above points as you do the form.
A simple test to see how well a student has established the "straight line" down through the hip and foot to the floor, and also how well he is able to establish "full" and "empty" in his legs; is to have him balance on one foot. He should be able to balance "comfortably" for 20 or 30 seconds with no requirement to use his arms for balance.
Another test is to stand first on the left leg, then turn the body and lifted right leg 45 degrees to the right and then back. Do this three times then switch to the other leg. All movement must be in the weighted hip joint (with a proper straight line down to the foot - no twisting the ankle or knee) in order to do this without losing balance.