In all my years of teaching and playing golf, the number one problem I see is grip pressure being too tight. It is amazing how people think they can swing their arms freely and powerfully holding the club as tight as they possibly can.
Hold the club in your fingers. If possible, keep it out of your palms, like throwing a fastball in baseball. If you throw a palm ball as a pitcher, that is a slow changeup. We want to swing fast. Almost everyone needs more speed. Yet they hold the club in a way that effectively keeps that from being possible.
Other problems occur when you hold the club too tight. Because you are making it almost impossible to release the club properly through impact, the golfer will lunge and try to turn their body awkwardly to try get some speed.
Also, use the smallest possible grip. If you have arthritis in your hands or wrists, ok. If you have large hands, use the least amount of grip you can. You have to be able to release the club, like cracking a bull whip.
Even women, with their beautiful, long fingers and elegant hands will hold the club so tight they can barely get it above their shoulders. I am always surprised at the amount of tension in their forearms. Realize you cannot control the clubhead through impact, so quit trying. Swing the club naturally and let your body hinge as it wants to. The correct way is actually easier.
Jeff Gibson PGA