Good posture is critical in making solid, repeatable contact and having a balanced and powerful swing. For the irons your feet should be shoulder width apart and with the woods you should have a stance that is wider than shoulder width. Your spine —  try to be straight as you can get it – I like to say “stand tall to the ball” — you are looking at the ball over your cheekbones instead of over your eyebrows — meaning – keep your chin up! This will help you turn your shoulders under your chin.  Also imagine a capital letter “Y” formed with your arms and club and a capital letter “A” formed with your head and legs.  You should have a nice tilt from the hips – like your are looking over the roof of a building instead of sitting on a bar stool. Weight should be in middle of feet, not on heels or balls of feet. This setup will help you turn back and thru better. Your posture (or spine angle), DOES NOT CHANGE in your golf swing. Your turn your shoulders on the backswing, and turn your hips around on the downswing, all the while keeping your posture and balance.  If you kept your posture and turned back and through to a full balanced, finished swing, the clubhead will get to the ball. It has to. Just don’t try to manipulate your hands and try to hit the ball – you are creating interference with your posture and you end up  flailing your hands and arms at the ball. Watch any tour player or good amateur and see how they keep there posture throughout their swing. They don’t collapse their front leg; they don’t flail their arms at it; they don’t stand up. Practice keeping your posture in a mirror and practice turning back and through. Now you are using the power of your legs and core- which will be transferred to your arms — and the ball will fly further and it will feel easier with less effort on your part. Now you have effortless power instead of powerless effort.