The moment of truth in the golf swing is when the club impacts the ball and using an impact bag will help you get the correct feeling of impact
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.
You might not have time to practice as much as a professional but you can have their set up in a matter of minutes, concentrate on keeping your upper body balanced on top of your lower body with your arms centered and not ahead of the ball