Before you begin any physical exercise, you must stand in Wuji Posture and clear your mind of other thoughts. This is similar to the attention practice, except in your standing practice, you will develop an awareness of your body.
Remember the story of the egg where “there was nothing but a formless chaos.” This is the state of Wuji. Before creation there was nothing, no form, no substance, just void and nothingness. All of existence was present at the beginning of time, and this sum-total of existence was aware of itself in its entirety.
While standing in Wuji Posture, your mind will probably fit the formless chaos definition of wuji; racing from thought to thought, but your body will be still; standing upright without moving. You want to stand until your mind is aware of your body, and clear from other thoughts.
Some teachers stress low or wide standing postures to develop strong legs. This creates a condition they call rootedness. Being firmly rooted means it will be more difficult to push you over, and you will have more power to push others away.