After my OW class I went and did the Nitrox class and the equipment specialty class. The rationale was that the Nitrox would be need for when I eventually wanted to go deeper. The equipment specialty course was completed to start to understand my equipment and what I could repair/ service without missing a dive (I have used the information I received on this class several times when "o" rings needed replacing). In the end the best thing to do is go diving and become comfortable with your equipment and being in the water. One other course that would be worth doing before going and completing the AOW would be peak performance buoyancy. I did a little of this on my AOW and learned a lot. I probably would have had far better deep and wreck dives during the course if my buoyancy was better (wouldn’t have used as much air).