Over the past 5 years as my son was preparing his way for high school baseball (and hopefully beyond) I've tried to read as much as I could on hitting, from Ted Williams "Science of Hitting" to Tony Gwynn articles on hitting. I've watch countless slo mo videos of great hitters to find out the common traits of a good hitter.
It dawned on me about 2 yrs ago that a great way of instilling the right way of hitting is to toss balls up in the air and hit. We did this as kids growing up, not knowing about proper technique, and I wonder if this helped us be better hitters?
If you break it down or just make a video of a person tossing a ball up and hitting it you will find that all the correct hitting techniques are incorporated in this drill. Quick hands, steady bat, hands inside ball at contact, hitting the ball at front of foot area.
I've used this technique this year to correct flaws in my son's hitting that he picked up from lack of coaching in high school and it corrected his swing within 2 weeks of constant reinforcement. Using wiffle balls allows one to be able to hit in your backyard without a net.
I think its best for a player to do the drill by himself instead of someone else tossing the ball as it forces the player to do more thinking about what he is doing.