'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.
Stretch in between sets as well.
Strides/Pickups - Short repeats at a 5K pace with recovery in-between. Each 'repeat/stride' should be about 20-30 seconds long and allow for a full recovery in between. Make sure you are properly warmed up-at least 10 minutes before the first. You are looking to get in about 45 left OR right foot strikes per 30". Multiply by 'two' for your RPM. So 45 left foot strikes per 30 seconds will equal 90 RPM, a running cadence that is the most efficient. You will typically be doing 4-10 repeats of 20-30" strides with a full recovery between sets (depending on the particular workout) by walking back to the starting point.