Start opening your chest as you're moving to take the shot, but don't exaggerate the movement too much. If you stretch/exaggerate the movement, you'll find it very difficult to move into place because your upper body will be rigid, and that will stop your lower body moving well. For higher levels of play, they will do this initial preparation, and then widen their chest right before they hit to gain a bit extra. Don't worry about this too much for now. It will come with time. Focus on a comfortable prep you can do while you move.