A casting drill to encourage very late rotation of the rod. Note how far my hand moves before the rod begins to rotate.
The correct application of power is one of the Five Essentials for fly casting. When we translate (drag our hand) before rotating the rod, we are a long way towards attaining that goal of "correct application of power."
Lay the line on the ground and drag the butt of the rod in the direction of the cast before finally rotating the rod to complete the cast.
Make sure you stop the rod high to form a good loop.