Those are good tips from Lou. It might also help to think of the good morning as a deadlift with the bar on your back.
Ball State's Strength Lab has an excellent video of the good morning. Click on Exercises OK -> Select the
upper leg/hip region then click on View Exercises -> Click on Good Morning - Arched Back -> Click on the link to the video at the top of the page.
Another tip that seems to help many of my clients is to pull the bar firmly into your upper back with you hands to prevent it from rolling toward your head.