Players learn how to shuffle in order to get their body in position to throw and to gain momentum toward the target.
Glove and Baseballs
Players pair up with gloves and 1 baseball for each pair. Since you want the players to gain momentum toward the target, make sure they have warmed up their arms and are making a long enough throw.
Have the player with the ball place it on the ground in front of him. He will then simulate fielding a ground ball. Once he has fielded the ball he will take a couple shuffle steps toward the target getting his body in good throwing position as he does so. After a couple shuffle steps he will step and throw.
Make sure the player is getting his body lined up as he performs the shuffle steps. His lead shoulder and hip should be pointing towards the target. As he gets lined up his back foot should land perpendicular to the target.