In freestyle swimming, when considering leg propulsion, think of your legs doing a flutter movement rather than a kicking motion. It should be the hip area which facilitates the action by going slightly down and up, thus creating opposition which helps in rotational movement and stability of the body. Do not allow your legs to over kick where the feet break the surface of the water or where the feet sink below body line. This would make you incur more drag than what is necessary. Train your focus on a more aggressive, compact and steady flutter kick.