When I met my teacher Master Pan for the first time he taught me these basic principles. He told me that: 'You will always benefit from these basic principles.' Later on, I found him telling every student in their first day starting Chen style Taichi. Here it is, after 20 plus years I still benefit from this principles.

The three principles

1/ Body aligned and vertical, top of the head floating, look far.
2/ Always breath naturally, exhale with the completion of each movement.
3/ Use as little muscle tension as possible but do not lose the correct configuration.

Pair of concepts

1/ Rigid and soft is what your opponent feels. If you follow his movement, there is no gap or bump in the contact, thus he feel you are not there, you are soft. On the other hand, when you got the right timing and configuration, you no longer follow him. If he try to move against you, he feels you are so rigid. In your point of view you just play your circles, you are still yourself. Chan Si Chin, a twisting type of movement that stretches and losses ligaments around joints. When success, combine this cycle of changes with relative speed relation control with opponent, one can demonstrate several dimensions of rigid and soft quality.
2/ Fast and slow. Fast refers to the instantaneous response to your opponent's move, and refer to your speed in reconfiguring yourself. Slow does not refer to speed defined as distance moved per unit time, it is the density of intention applied in movement. Every movement is seen to be composed of succession of incremental frames. At each instant there is frame with Taichi configuration. Slow means patiently detail those instances that happened along the path of movement. It seems 'slow' because of the richness or fullness of the movement.

And a commitment

The art of Taichi has no end to it's depth. It demands a great deal of commitment to go through a lifetime of practice to perfect it. We must understand the difficulty ahead so that we can prepare and improve ourselves though everyday life.