Removing the bad habits is vital. Many really good wrestlers are getting away with sloppy execution because they are facing competition that isn't that tough. When they start having tough matches every time they step on the mat(college) it is so frustrating when their "bread and butter" moves aren't going anywhere. Take my word for it.

Footwork, hand control, and head position are the small basics that really should be stressed.
Jumping rope is a very important basic workout that has recently helped me control my steps so I don't get off balance when I'm trying to create an angle, and I have more control of my penetration step, especially when shooting through the man (which most high schoolers aren't doing!)
Those are my thoughts from personal experience. I think the main goal should be making the transition from high school to college as smooth as possible, and remove the necessity to go backwards for some kids in order to breadk those bad habits.