Try to go as slow as your creeper gear will allow and get a BIG bottle of advil, your neck and shoulders will be killing you when your done. I tend to start of the high side and set my first pass as straight and to grade as i can, in your situation, then slowly take a half of a width pass and watch the side of your blade that is on the finished side adjusting the height almost constantly. I will agree that tilling or some times using a pulverizer is a much better way. The shale in your yard could make that almost impossible or dangerous in your case.