When you cannot hold the body still, you cannot hold the brain still. If you do not know the silence of the body, you cannot understand the silence of the mind. Action and silence have to go together. If there is action, there must also be silence. If there is silence, there can be conscious action and not just motion.
B.K.S. IyengarYou must do the asana with your soul. How can you do an asana with your soul? We can only do it with the organ of the body that is closest to the soul - the heart. So a virtuous asana is done from the heart and not from the head. Then you are not just doing it, but you are in it. Many people try to think their way into an asana, but you must instead feel your way into it through love and devotion
B.K.S. IyengarFocus on keeping your spine straight. It is the job of the spine to keep the brain alert.
B.K.S. Iyengar