Pull Drill - Focus will be on learning to 'catch' the water with your forearm and pull yourself through the water. If you feel your lats (the muscles under your arm pits that go down the side of your back) engage, then you are starting to get it. If your shoulders are tired, then you are still using too much shoulder and not enough lats.
(*) B.P.A. = Best Possible Average, this will be one benchmark set that you can do once every three weeks. The idea is to record the 8, 100's and average them. Keep the record and you should be slightly faster the next time.