1. Keep your eyes on the ball until AFTER impact. Not only to envision the ball’s position and depth so you may come on contact with the ball, also because looking at the ball will help to stabilize your swing. Your head is connected to your shoulders, and turning your head on the backswing will sometimes lead to overswinging because your shoulders will have freer backward movement.

2. To prevent overswinging, consciously stop your backswing when your left arm is horizontal against your chest. This will give you control over your swing and as an amateur, if executed properly this will give you more than enough power to hit the ball.

3. When swinging, it is mostly shoulder movement. On the backswing your left shoulder should move to the center as your back is turned and your eyes are still on the ball. Then as you swing down, the right side should replace the left side as you impact the ball.

Good luck and hope my answer helps you.
References :
competitive golfer