To work on reading and reacting to a ball hit into the outfield, try the four-cone drill.
Start with four cones that are evenly set apart in a square. The cones should be approximately 10 feet apart, with the player in the center of the square. From there, a coach or teammate will indicate whether the ball is in the air or on the ground and whether the ball is to the left or right. To simulate a fly ball for example, the coach would point up into the air with their right arm or left arm to indicate direction. For a groundball they would point toward the ground, again with either their right arm or left arm.
The outfielder would then react to the fly ball by going back to the cone behind, on either the right or left side, as indicated by the coach. For a ground ball, come up to the cone in front on either the right or left side, as indicated by the coach.
Get to the cone in an athletic position, keeping your feet active. The coach can determine at what speed you should perform the drill (50%, 75%, game speed). To enhance the drill, just add a ball or stretch the cones to develop your range.
Reading the ball off the bat and making a quick reaction will be key to outfield development.