The secret to standing in zhang zhuang or yi quan is not in how still you can be, rather how you adapt and adjust subtle energies in the body so that you will be relaxed yet strong, calm yet alert. Trying not to move can create tension and defeat the purpose of standing. Start with the muscles and look for where energy is not flowing freely. If not, then you are holding on to something that hinders flow.
Another secret is to understand the concept of “two bodies”; one energy and the other physical. Separate them as yin and yang separate, but remain as one.
You can incorporate standing principles when you pause in a posture in the form; then maintain the sense, or sensation cultivated in standing, as you move through transitions from one posture to another. That alignment, central equilibrium, zhong ding, qi going through and circulating through everything is the essence of taiji. Susan A. Matthews refers to this as “stillness in movement.” Wuchi never goes away even thogh you ar moving. Very yin-yang.
Don’t know what standing, or Zhang Zhuan, refers to? You can learn more by reading The Way of Energy by Lam Kam Chuen. I downloaded recently it as a pdf here.