Congrats Ragdoll - I just got a 5060, and am really excited to try in underwater this spring.
I think the most important thing is to get completely familiar with the camera in the housing, so you know what the camera is capable of doing, and more importantly is not capable of doing underwater.
Take some richly colored items in the pool with you, and see what range the flash is really effective at. Keep in mind your digital zoom will take you much closer to the subject than the light of your strobe can travel - get to know your strobe's range. One trick is to put a long rope with tick marks every 6" or so, so you can see how the light falls off.
Bring some little toy fish, and practice with the macro lens to see how close you need to be to get good shots (it helps if you have a dive buddy jerk them around in the pool, like a live fish moves).
Juggle your ISO, speed and f stop combinations to see how the image quality is affected by faster (more forgiving) camera settings.
I'm not sure if you have an external flash, but try it in auto and manual modes, at a number of different targets, to see which is best for the type of shooting you plan to do. Fiddle with the exposure value compensation to the point where it is second nature in the field.
I also think one of the biggest things UW photographers overlook is their buoyancy control. The task loading of adjusting a camera often makes even practiced divers bounce all over the place, especially when focused on a moving target with some current. Spend some time getting comfortable working with the camera while maintaining perfect neutral buoyancy. This also helps you get much closer to fish - you have to move with overly exaggerated slow motion and very shallow breaths to get close to a lot of skittish fish. Place an inanimate subject on the bottom of the pool, and practice working your way towards it with minimal fin kicks, shallow exhaling and as motionless approach as you can, all while adjusting your camera.
Best of luck!
Philip Lewin
