You often hear a coach tell a player to keep his eye on the ball or watch the ball hit the bat. While that can't be done liertally, it should be practiced. Here's a drill:

Since hitters tend to move their head when hitting the baseball, a great drill is to put colored masking tape on the balls and have the player stand in the batter’s box and track the ball into the catcher’s mitt. Once he recognizes the color, he should yell it out such as “Red” or “Blue” etc. Once he does this for a few pitchers, have him swing but he must still yell out the color when the bat makes contact with the baseball. This forces the player to focus on the ball and he will learn to keep his head from turning at the last second.