“Composure” is a term that I find useful to describe the state of being while practicing tai chi. The specific movements made matter very little, what is important is to maintain composure while doing them.
The elements of composure are many and subtle, but the main indicators are posture, breathing, relaxation, and focus.
Posture: Are you aligned with gravity? Are you rooted? Are you stable?
Breathing: Are you breathing naturally? Abdominally? Smoothly?
Relaxation: Are you straining? Are you floating? Are your joints expansive and flexible?
Focus: Is your mind clear? Are you aware of your body? Are you perceiving the present moment?
It is the epitome of tai chi practice to maintain composure throughout the practice session, and to break it only gently at the end. Best of all is to avoid breaking it altogether, but instead to carry it with you throughout your day. But certainly beware of breaking it during practice. Observe when distractions and internal interruptions break your composure, and notice the distinction when it is lost. The more acutely you can notice the distinction, the more actively you can maintain your composure under all circumstances.