this pretty much sums up the theory in that its not about picking up the ball as your opponent hits it (although i would never dismiss this skill if you have it) it is more about putting yourself where you would most expect their next shot to go, put yourself in the best position to cover the territory that you should be covering.It's not just about reading shots but realizing that unless you're playing Djokovic, your opponent is probably very limited as to where he can hit any given ball. I'm 40 pounds over my playing weight but I can still get to most balls simply because I don't stand there believing my opponents can hit the ball anywhere. I cheat to a certain side and if they go for a winner to a spot I'm not worried about, they miss 90% of the time anyway. Haven't totally analyzed it, but I think I simply cheat that they're going to hit crosscourt most of the time.
I agree with you about watching the racket face. In the past before the SW grip, windshield wiper follow-through, and high velocity racket head speed, it was fairly easy to tell where a player was going to hit the ball just by watching the path of the racket head prior to contact and after contact. If a player has more traditional strokes you can still read them pretty easy. The tricky part when trying to do this is that you have to briefly take you eye off the ball and watch their racket head.persistant,
I recommend watching the racquet face of your opponent. But as the others have said, it comes with experience above all. When you get enough experience you will know where the ball is going, sometimes before they do. Then you can use it against them. It just takes lots of court time and paying attention( which few do in practice).