The single most important thing about running form in terms of efficiency is where your foot strikes the ground relative to your body. Heel strikers tend to stride out in front too far and actually cause a loss in momentum. Mid foot strikers tend to land with their foor under their hip and maintain momentum throught the stride. There are people that heel strike that still land with their foot under their pelvis and are very efficient this way, but they are the exception to the rule. As for running on the treadmill, if you're running closer to the front or using even a slight incline there will be a tendency to land more towards the fore foot.

As for shoes. Get out of those cross trainers!! Running in cross trainers for anything other than short treadmill runs is asking for a tendinitis in your lower leg because the shoe is too stiff to allow for the normal torsion through the foot that occurs with running. That means your foot is constantly working against the shoe. The other thing is that you need to be properly fit. Fit is the one most important thing in biomechanical efficiency. More so than getting a shoe for a pronator or supinator. If you're not comfy, you change your natural stride and any other biomechanical advantage you get from the shoe goes out the window.

Hope that helps.