One area of great importance to me when I am analyzing a student's swing is to look at the elbows. How the elbows work within the golf swing is extremely important. Another way that you might relate to this is when you read about the term connection.
I make sure the student is aware of the distance between the elbows at the set-up. Then as you take your backswing, I recheck the distance between the elbows at the top of your swing. Usually the elbows have separated at least 6 to 12 inches! This separation, or disconnection, causes a number of things to go wrong on the downswing and through impact, the critical moment the club meets the ball. I also check the distance between the elbows at the finish. The separation at the finish is a big indicator of what actually takes place through the impact and beyond.
I like to promote that the distance between the elbows at the set-up needs to remain the same throughout your entire swing. In other words, they remain the same distance apart at the top of the swing, at impact and at the finish as they were in the set-up. One of my favorite drills I like to challenge my students with is to get a large car sponge that you could purchase at the auto store or a rolled up towel and place it between the elbows at your set-up. Your challenge is to make your full swing back and through to the finish without losing the sponge! It's a great drill and a difficult one at first, but the more you do practice swings with it you will eventually achieve the connection that is important to a more square contact with the ball and clubface and that, in turn, creates straighter and longer shots.
Give it a try and let me know how you do.
Linda Gaudi PGA, LPGA T&CP