Regardless of the style, stepping and stances are of the utmost importance. It is the source of consistent firm stability in motion that makes the ability to issue energy effectively possible.
In this video, Yang Jun Laoshi clarifies the Fixed Foot stepping method.
feet, legs, and waist should act together
as an integrated whole,
so that while advancing or withdrawing
one can grasp the opportunity of favorable timing
and advantageous position.
If correct timing and position are not achieved,
the body will become disordered
and will not move as an integrated whole;
(the correction for this defect
must be sought in the legs and waist – take note of this). – from the Tai Chi Chuan Ching attributed to Zhang Sanfeng