A tension filled grip, especially from having the shaft too much in your palms, will kill your entire swing. It stops your wrists from hinging naturally and then works its way up your arms and into your shoulders and locks up your entire swing.
Making mini swings with your elbows glued to your body will give you the correct sensation of the large torso muscles swinging the club, not the arms
Maintain a constant posture throughout the entire swing so that your body does not move towards the ball during the swing and cause the heel of the club to make contact with the ball