It is advisable to have one partner at a time lead the exchanges in the beginning. Follow this with the freestyle method of exchanging where either person may choose to change the direction of the pattern between yin and yang.
The following exercises will be the vertical yin-yang circling patterns using both sets of hands on the ball, followed by each person using a single hand attached to the ball. When practicing the exercises using both sets of hands, the ball will be turned slightly along its horizontal axis allowing a crisscross pattern.
More of these exercises may be found Tai Chi Ball Qigong For Health and Martial Arts.
1. Stationary (Ding Bu)
The first exercise is the vertical yin-yang circling pattern while in a stationary position. The circling pattern as well as the exchanging between yin and yang are performed the same as you have done when practicing solo. One difference is that while you move in a yang direction, your partner will move in the yin direction. The opposite holds true when you move in the yin direction.
To start the exercise, stand in ma bu facing each other. With both your hands holding the ball in front of your dan tian, rotate it slightly and allow your partner to place both their hands on the ball. Begin to vertically circle the ball in a yang direction and expand the size of the pattern until you have reached a mutual maximum range of motion.
Continue to vertically circle the ball a few times, and then move on to your yin-yang exchanges. You may elect to execute the exchange anywhere in the pattern. Once you are able to execute the exchange smoothly, allow your partner to perform his exchanges until it can be done smoothly.
Follow this action by allowing either person to lead the exchange in a free-style manner. You may also elect to close your eyes to reach a deeper stage. Continue to practice this pattern until you are both able to perform the circling with exchanging, seamlessly, anywhere within the pattern.
2. Rocking (Qian Hou Dong)
The next partner exercise is the yin-yang vertical circling pattern while rocking. To start this exercise, face each other standing in si liu bu with the right foot forward. Your partner will place both hands on the ball while you hold it in front of your dan tian.
Initiate the vertical circling pattern in a yang direction, while rocking just as you have done while solo. Your partner will be rocking while circling the ball in the yin direction. Keep in mind that each time you and your partner rock backward you should be careful not to allow the ball to get too close to your body. This can cause unnecessary muscular tension resulting in restriction of the flow of qi. It also is not a good defensive position. Practice the vertical circling pattern until you and your partner are comfortable with the movement. It should be smooth and there should be no bumping throughout the rocking pattern.
Next, practice your yin-yang exchanges. Practice using a few different methods. First, practice the exchanging by allowing one person at a time to lead the exchange. Follow this exercise with a free-style exchange exercise, where either partner may initiate the exchange. The passive partner trains to follow the lead of the active partner. The active partner trains his awareness of how to initiate the exchange.
Finally, practice the exchanges in the following manner. Your partner will move the ball toward the center of the pattern, then directly toward the center of your body. You will yield to the incoming force and neutralize it by rocking aft and redirecting the ball in a different direction. Once you can perform this smoothly, allow your partner to perform the same task.
Follow this with free-style exchanging between partners. Continue to practice this until you both are able to perform the exchanges smoothly and without interrupting the pattern. Also practice with your eyes closed.
3. Stepping (Dong Bu)
The next stage is to practice this while stepping forward and backward. Begin this exercise facing your partner in si liu bu, either leg forward. With both sets of hands on the ball, start your yang vertical circling. Increase the size of the pattern to the maximum range, and then add stepping forward and backward across the practice area.
Once you and your partner are able to move back and forth smoothly, move on to the yin-yang exchanging. First, have your partner continuously step forward while you execute the exchanges. Next, you step forward and allow your partner to execute the exchanges.
Once you and your partner are comfortable with this stage, begin to step forward and backward, and this time, both of you are allowed to initiate the exchange of the pattern back and forth. Pay particular attention to your following jin, connecting jin, as well as sticking jin while your partner steps backward. Continue this exercise until you have crossed the practice area several times. Remember to keep an equal distance between you and your partner.
The last stage is to practice this same exercise with your eyes closed. As before, this will enhance the sensing jin by taking away the element of sight.
In the next set of exercises, each partner places a single hand on the ball. The opposite hand should initially be placed on your dan tian. When you are comfortable with the exercise, you may place the second hand on your chest to assist with feeling the opening and closing of this area.
Next, practice the same exercise with one hand out to the side approximately level with your dan tian.
Finally, you may practice the exercise by placing the free hand near the elbow of the hand on the ball.
These patterns should be practiced while stationary, rocking, and stepping. In addition to the single hand exercises, practice switching hands. Do this by placing the non-active hand on the ball while performing the pattern. Once that hand is placed on the ball, rotate it on the horizontal axis while simultaneously lifting the other hand off the ball.
The above excerpt is from Tai Chi Ball Qigong For Health and Martial Arts by Dr. Yang, Jwing-Ming and David Grantham.