Myth - Bring the racket back as soon as you see the ball coming toward you.
Truth - Although on paper this sounds good, the pros do not take the racket back quickly. Are you surprised? Watch the pros and see what you think. In fact, if he were taking a conventional tennis lesson the teaching pro would tell him that he is taking the racket back too slowly! The truth is each pro has his own timing, but most pros take the racket back when they are about to hit the ball, not as they see the ball coming to them.
One of the reasons the pros do this is because it is more natural to run to meet the ball with the racket in front of them rather then behind. The pros may have a slight turn with the racket in the direction they are running, but the full swing begins when they are about to hit. I usually demonstrate to my students how silly it looks to run to meet the ball with the racket wagging behind. Then I ask if they have ever seen a pro look like that. They usually laugh.
Another reason the pros wait to take the racket back is because the back swing is part of the timing, the rhythm, and the power of hitting the ball. If the racket is back too soon they will become too mechanical and lose the timing, the rhythm, and the power of their shots.
The lesson here is to not take the racket back too soon. Wait until you are near the ball and about to swing. If I were you I would not even think about taking the racket back and let it happen naturally. The more you practice letting the racket go back naturally, the better your timing and rhythm will become. Do not fall prey to the myth of taking the racket back to soon.
You have just had your first lesson in theoretical knowledge versus application knowledge. You should always choose application knowledge. This will help you learn to think and play like the pros.
I guess the question you may be asking is how do I know when it is theoretical knowledge and when it is application knowledge. The answer is, in one short word - ME! My web site, email tennis lessons, books, and audio tapes. You didn't think I was going to let you come to my web site and get away that easy did you? Sorry, you are stuck with me.