Get your hands on the club properly and learn the correct grip pressure by sliding two tees between your thumb and forefingers and hitting balls without dropping the tees
Focus on your left wrist at the top of the backswing and start of the downswing to get to impact properly, many players have a cupped left wrist which changes the angle of the clubface, this causes an open clubface and results in casting and manipulation during the last portion of the downswing
Tension is by far the biggest killer in the golf swing, gripping too tightly, standing in your set up too long, you need to keep your body in motion and relaxed to properly strike a golf ball