This article is based on 36 years of personal experience and dedicated study with Master Alex (Da De) Dong and Master Tung Kai Ying. The following Taiji principles are true at all times.
Lift the crown. Do not lift the head. Lift the crown by reaching upward slightly with the scalp, the skin on the very top of the head. Do not lift the head up with the neck. Do not lift the head by raising the nose or eyes or any other trick you may have devised to lift the head. Don’t lift the head; lift the CROWN of the head. You can check to see if you are lifting the crown correctly. When the crown of the head is lifted, the upper mandible will be lifted . The whole face and jaw must be relaxed and the tongue rests comfortably on the roof of the mouth. It is normal in our daily life for the head to rest or sit on the neck. When the head sits on the neck, the upper mandible will sit on the lower mandible or hang down from it. When the crown is lifted you get feeling of the upper jaw rising, not a feeling of the lower jaw hanging. In Taiji, lifting the crown separates the upper body from the lower body. This separation is essential even when the head and body are not upright as in the posture “Needle in the bottom of the sea”. If the back jaws are touching, the crown of the head is not being lifted. Try this and check to see if you are indeed “lifting the crown”. When the crown of the head is lifted, the diaphragm drops, the chest becomes empty and the lower belly expands. The eyes move with and in the direction of the movement which includes the down directions. Move the direction of the eyes to match the movements of the forms but do not raise and lower the head to do this. The eyes can move independently of the position of the head. Lift the crown continuously throughout the forms and during push hands, maintaining the separation of the upper body from the lower body. Lifting the crown raises the spirit (shen), it raises your awareness.
When doing the forms, do not think about other things, be in the moment. Think in the direction of movement, this will help keep you focused in the same way that some meditation styles focus on a mandalla pattern or a sound to stay focused. Stay focused, do not daydream or become distracted. When doing the forms, there will be many distractions, sounds, sights and mostly thoughts. Do not attach your attention to these things, let them go. The distractions are there but they are not there. Sort of like "Wu ren rou wu ren". Keep your spirit soft (Yang Style). Soften and relax your mind and your entire body. Relax and soften your face, your mouth and shoulders, fingers, belly, hips, toes, your thoughts, all the joints of your body, everything. Now that you are softer, soften inside, soften your “spirit” and soften everything even more! These things are essential for the meditation of Taiji.
The mind, intent (will) and eyes slightly precede all movement. Think in the direction of movement; look in the direction of movement. When moving forward, the eyes, mind and intension are just a little bit ahead of the movement but at the end of the forward movement, the intent and eyes extend quite far ahead at eye level. When the direction of movement retreats, the mind, eyes and intention also retreat and reflect inward.
Both hands use split energy in every movement, at all times. (I find one exception to this fundamental, the Beginning and ending movements. I don't see split energy in these movements. I do see the split energy between the hands in all the other movements.). There are two kinds of split energy. One is the opening into opposite directions between the hands. The other is the closing, the gathering, the pressing of the two hands into and toward each other.
The first kind of “opening” split energy is always initiated by first pushing down or pulling back. Never lift a hand upward without first pushing down with the opposite hand. Never move a hand forward without first pulling backward with the opposite hand. The Yin hand gives energy to the Yang hand. You can further understand this principle with this example: Imagine a pipe in the shape of a “U” and the diameter of your hand. If this U shaped pipe was filled partially with water, the water would distribute itself to an equal level on both sides. Put a hand on the water of each side of the U shaped pipe. Raise one hand and notice that nothing happens to the water. Push down on the water with one hand and notice that the water on the other side of the pipe rises, which then pushes up the opposite hand. This principle also applies to the manipulation and movement of energy. Push down with one hand and energy naturally moves into and fills the opposite hand, expanding and moving the hand upward. This is the same principle when moving the hand forward. First pull with the hand going backward to generate the energy to move the hand forward. The breath will inhale slowly as the arms and hands are filling up and separating, but the breath will exhale as the hands finish the outward movement. This kind of breathing will happen naturally if you let it. Stand in front of a mirror and in a stationary stance, move your upper body with the "Cloud Hands" movements. Watch to see if the hand going down moves first or if the hand moving up begins to move first. Try doing this: First start to move the bottom hand up and then move the top hand down. Next move the top hand first and the bottom hand second. See if you can feel the difference.
The other type of split energy is when the hands close toward each other as in “Close Hands”, “Roll Back” or “Press” instead of away from each other as described in “open split energy”. The hands move toward each other at the same time, both hands pushing inward, one hand pushing toward the other as though pressing into opposite sides of a ball. The breath always exhales when the hands close toward each other because it is a sinking or gathering movement, where the energy is being condensed and brought to center. Soften slightly the yang hand/arm after it has executed its posture. Fill up to go out, soften to come in. Open with filling energy and close with softening energy in every movement. All transition movements use soft. closing and gathering energy.
When moving forward, the hand moves forward away from the body, this brings the elbow forward which brings the shoulder joint forward.
The shoulders and waist work together, one cannot turn without the other.
Hands and feet match. Knees and elbows match. Shoulder joints and hip joints match. When does the body begin to move forward? The body will move forward when the shoulder joint starts to move forward, i.e. after the hand moves forward which brings the elbow forward which then engages the shoulder joint. Shoulder and hip joints match, so the hip joint will go forward at the same time as the shoulder joint goes forward and that is when the body moves forward..
When moving forward, gradually sink into the hip joints by the time the body is half way between the front and back foot. At the half way point, finish sitting, sinking into the hip joints and continue to sink the hip joints into each foot. Sink physically and with intent equally into both feet. Always have equal intent in both hands. Always have equal intent in both feet. Yin and Yang are equal in intent. Yin is not less than Yang.
To understand the concept of “sitting”, try slowly sitting into a chair. Notice that first you put your bottom onto the chair. Then watch as your whole upper body settles, relaxes down and into your hips and into the chair. This is the feeling of your body as it settles down into your hips (your Kwa) and spreads equally and a little bit heavily (strongly) into both feet. This sitting into both feet will cause the breath to exhale.
At the end of the move and after sinking into both feet, complete the forward movement by pushing slightly into the ground with the back foot. This will cause the breath to inhale and bring the energy up from the ground, causing the Tan Tien to roll slightly forward, up and then back around down toward the end of the spine, causing the buttocks to tilt down and under. These things will cause the energy to naturally fill up and straighten the back and this movement will cause the energy to “fill up” into the hands. It is important that the buttocks are dropped as the hands issue the energy. Watch in a mirror, if the buttocks do not drop down and slightly back before the hands move the last bit forward, issuing the energy, then you need to question your technique.
When moving backward, first move the hip joint and shoulder joint backward together. Do not move with the outside of the bones, move with the inside of the joints. You can feel this by putting your finger into the kwa and pushing with the finger back toward the back foot. When you move backward with the hip joint, the sinking and rolling of the tan tien engage near the beginning of the movement so that by the time the backward movement is complete the hips are already sunk. When you wrongly move the hip bones (not the inside of the joints) backward, the sinking doesn’t happen until the end of the move. Move the joints, not the bones.
The shoulder joint brings the softened elbow backward which then brings the hand backward near the body. All movements going backward or into center soften and relax while bringing the arms and hands closer to the body. The trunk of the body will also compress on an inward sinking into center part of a movement. The mind and spirit also reflect into center. When a posture is in the back position, the intent is still equal in both feet. The weight is different between the feet but the feeling of intent makes them feel as thought there is equal weight. The upper body settles into the sunk hip joints before continuing into the next movement. Settling takes time.
Always step forward with about 2-4 inches of space between the inside of your heels. The front foot always points the direction you are going. Step only as far (long) as you have the strength to immediately withdraw your forward foot (without having to shift your weight backwards). Step out with the heel, commit intent into the ground with the heel without committing any weight; unflex the ankle and push the foot down to the ground (like pushing on the accelerator of a car); after the foot is all the way down and connected to the ground energetically, then you can start to transfer weight onto it, moving your body forward. Step backward in a smaller step than a forward step. Step backward with the inside oif the heels in line, no space between the inside of the heels. Think of it as an elongated half step. Step backward with the toe first and gently bring your whole foot down so that you back foot is more than 45 degrees and less than 90 degrees from the direction of the front foot. This is the direction of the back foot in every movement.
All half steps are at the instep of the back foot, the foot you are sitting on. The half step foot will always point the direction you are going (it is the front foot). In a half step position on the toe, the toe slightly touches the ground. The purpose of a half step on the toe is a holding move, waiting to see which way you are going to step, ready to move but uncommitted as to where. This is especially important in moving push hands. A half step on the heel is very different. Half steps on the heel are almost empty of weight but energetically the intent in the heel is strong. There is no weight but it will feel like there is weight.

Author's Bio: 

Toni DeMoulin practices, studies and teaches Taiji, Qi Gong, and Push Hands. She is a student of Master Alex Dong and hosts Alex's workshops in Santa Barbara twice a year. She started the Santa Barbara branch of Tung Ying Jie Taiji Legacy- Alex Dong International Taijiquan Association in September, 2003 and was instrumental in bringing Master Alex Dong and his taiji to the Czech Republic in May 2006.
Toni initially studied with Alex's uncle Master Tung Kai Ying (from Spring of 1972 to September, 2002). He was inspiring and a significant influence in her studies and teaching. Shei started Tung Kai Ying schools in Santa Barbara, CA (1976), Ojai, Ca (1988), San Diego, CA (1988), Rancho Bernardo, CA (1990), and Portland, OR (1994). Toni has also taken workshops with William C. C. Chen, Al Chung-Liang Wang, Chris Luth and Don Miller.
Helping other students and teachers to discover the invisible aspects, the energetics of Taiji, and to enjoy Push Hands are of special interest to this Taiji grandma. Today, Toni teaches regular classes in Santa Barbara and gives Taiji, Push Hands and Applications workshops by invitation to groups and schools worldwide.