Maintaining the same posture throughout the swing is critical to hitting the ball in the center of the clubface
Practice your entire swing in super slow motion, this will allow your mind to focus on the correct muscle movements needed instead of trying to make your brain work on the correct movement while you are swinging, just do it don't think it
Casting, heaving and throwing your club on the downswing result in a tremendous loss of power because you release the club too early and exert the energy of the swing in the wrong location