The best training aids are those they let us practice ball trajectory and ball distance. If we execute a nice beautiful looking golf shot but it does not go the right distance at the right trajectory we could have some unfortunate results (short in the bunker or maybe even over the green).
I like line or ropes on the green so we can work on our distance. I also like to create windows out of PVC pipe in order to help students work on ball trajectory.
Final the most neglected tool – is your brain and eyes. We must be able to see and visualize before we can create.