One of the complexities of backstroke is that you're normally doing two things at the same time: a recovery with one arm and a stroke with the other. An innovation Terry introduced in the Backstroke DVD is to simplify this by practicing with only one arm at a time, so you are doing only one arm movement at a time.
Once you've mastered head lead and hand lead sweet spot, the one-arm stroke is just a matter of switching from your head lead sweet spot on one side to your hand lead sweet spot on the other side, and back again. This keeps your focus on using your core body rotation to power your arm movement while maintaining balance and streamlining.
Once you've practiced that on both sides, transitioning to full stroke backstroke is just a matter of combining your arm recovery on one side with your arm stroke on the other, and vice versa.