If you're trying to break 100, you probably need a better understanding of the basic swing motion. Many golfers lift their arms to the top (below, left) instead of making a full turn with the hips and shoulders.
The backswing should begin with the hands and arms swinging away from the ball, which turns the shoulders and then the hips (left). From the top, the lower body starts forward, which drops the club to the inside on a powerful path.
An arms-only backswing leads to a steep crash at impact. The arms should swing and pull the body into action, the shoulders turning 90 degrees, the hips 45.
Here's an image for ensuring a square clubface and hitting straighter shots: Picture your arms and shoulders forming a triangle at address. Keep that triangle intact as much as you can during the backswing and again through impact. (Eventually the right elbow folds going back, and the left elbow folds swinging through.) When your elbows pull apart or your forearms crisscross, the face angle changes. To keep the face square, monitor that triangle.
