Part 1 - Lower Body
Understanding position and movement of the legs 
during the Part 1 of Our Tai Chi set. 
I utilized some painters tape to indicate the placement of the feet during these section of the set. Feel free to do the same thing at home. Note that the placement of the tape may vary depending on the height and range of motion of the individual. Utilizing some painters tape may help with the foot placement and makes it easier to verify if we are missing a step or if one of our feet is "in-stepping".
In-stepping is a common source of instability and loss of balance. If you are in-stepping on a regular basis (without even noticing), you will also be doing it during your Tai Chi practice. And inversely, if you become aware of this situation and correct this unfavourable habit during your Tai Chi practice, it will have a positive effect on your everyday stance and movements.

This picture shows an in-stepping position. The back heel is on or crosses the line of the front foot. This type of stance contributes to instability and loss of balance.

This picture shows a more stable position of the back foot. You are welcome to utilize even a wider stance during your Tai Chi moves to create more stability. Listen to your body and decide on a daily basis how wide your stance should be.

IMPORTANT: If you are in-stepping, which one of your feet is actually in-stepping, is it the front or the back foot? To help you answer this question, ask yourself which foot was the last one to move. That is the in-stepping foot and thus, that is the one you need you correct.

Finally, here is a superior view of the painters tape pattern.