Key principles

A tai chi instructor should possess these generic skills:

1. An understanding of the following:
   - The Art of War
   - Chuang Tzu- I Ching (Book of Changes)
   - how to teach
   - mutual arising
   - Tai Chi Classics
   - tao
   - Tao Te Ching
   - te (essence)
   - tzu-jan (of itself so)
   - yin/yang
   - zen
    
2. The ability to explain and demonstrate:
   - 13 postures
   - 4 ounces of pressure
   - 6 balanced pairs
   - change
   - chin na- fa jing
   - folding
   - groundpath
   - jing
   - mushin (surrender/immersion)
   - neigong
   - opening & closing
   - reeling silk
   - shen (emotional content)
   - sinking & rooting
   - softness
   - substantial & insubstantial
   - sung
   - weaponry
   - wu nien (not preparing)
   - wu wei (not forcing)
   - Yang Cheng Fu's 10 essential points
   - yielding
   - zanshin (continuing mind)
    
3. The application of the tai chi principles in self defence:
   - without emotion
   - without being tense
   - without opposing the incoming force
   - without necessarily hurting the assailant

These precepts are not something that you can expect to master overnight. They are what make the art 'tai chi'.
The list is not comprehensive.