hold a solid stand to help you keep sitting back, watch lower legs and knees, the whole move is on Kwa, pull the legs into pelvis when sitting and standing.
make sure you use Kwa only, pelvis and waist are not involved, 確定只用胯來做,骨盆與腰都不動。
follow to practice but not too much, don't ever let front knee move over ankle .跟著練練看,但不要太累了
control legs from hip joints or you will hurt knee, 用胯轉腿,否則易傷膝蓋。
follow the weight to squat, release arms. 
put weight on hip joint, never on knee, keep straight.重量放在胯上,永遠不要放在膝關節,保持身體直立。
keep spine straight,  knees still and the lower leg vertical to ground all the time 保持脊椎正直,膝關節穩定,小腿垂直於地面。