Many golfers can not get into a proper set up position and posture because their hamstrings are too tight to allow the straightening of the back, so before you tee off or practice work on stretching out your hamstrings so that you can work the golf swing properly around a straight back
Hold one arm out with your palm down and with the other hand push all five fingers up and back to stretch the flexor on the bottom of your wrist
We are looking to create a clubhead that is traveling down to hit the ball, so take your address position and straighten out your left knee, this will bring your hip back, move the shaft forward and straighten your left wrist