Robert99, He would have practiced his skydiving. Unless he had advanced training, it is unlikely that he was able to practice at night, and very doubtful that he would have jumped in high winds and rain. What skydive centers were open in 1971?
My skydiving career was short and covered only a very few years in the early 1960s.
Frankly, there is very little training that Cooper could have had that would have helped him during the hijacking. The jump was made at night, with a complete overcast and several cloud layers below him. There was light rain below the overcast but nothing is said in the records about what the cloud situation was above the airliner when he jumped from 10,000 feet.
It is highly probable that Cooper tumbled immediately after leaving the aft stairs and it would be nearly impossible for him to stabilize in any manner. Consequently, he would become disoriented in the space of a few seconds and that would increase the probability of him being a no-pull.
As 377 has pointed out, the best course of action would have been for Cooper to pull right off the stairs. But there is nothing to even remotely suggest that Cooper did so.
In the thread about the flight path, I have pointed out the only possible means - repeat, only possible means - to explain what happened to Cooper and how the money got to Tina Bar without having to require several miracles.