One of the biggest challenges encountered by youth baseball coaches is the difficulty that players have in following and identifying the pitch. In younger players, a common problem is that the batter doesn't pick up the ball until it is too close to hit. In older players, the issue is more that the batter doesn't identify the pitch until too late, leaving him at the mercy of his pitch guess.
The solution to both of these issues has a similar fix - get the hitter concentrating on the pitch as early as possible.
But how to accomplish this? You can tell the player to "watch the ball" until you are blue in the face, but odds are that they won't connect what you are trying to convey.
Take a selection of baseballs and, using a marker (colored sharpies work great for this), draw coin-sized colored dots on the surface of the ball. Repeat the process with at least one alternate color, making sure that it is clearly distinguishable (red and blue work well for this).
To begin with, pitch to your batter from regulation distance, but instruct them to not swing. Instead, have them call out the color of the dot on the baseball as soon as they can identify it.
As the hitter's recognition improves, call out a certain color and only allow them to swing at that color ball. In all cases, make sure to mix up the colors used (this is why three colors are better than two), and hide the ball in your glove until you actually begin to make the pitch.
What have you accomplished? Your players are truly watching the ball from the very instant it leaves the pitcher's hand, giving younger players more time to nail down their timing, and older players more time to recognize the movement of the pitch. It goes without saying that players of all ages can benefit from this drill.