Ikelite housings rock. 99% of them give 100% coverage on the camera controls, if you see what I mean.
So the most important thing is to get used to your camera, shooting on land. And shoot a lot in dim light, to simulate shooting down under.
Doing some shooting with the camera in the housing, so you can see how it acts as far as shutter half press feel, and in terms of flash blockage is a good idea.
What camera are you using? Are you planning to use an external strobe?
A ur-pro or magic filter might be helpful too, to get better white balance, when you're down lower than 10 feet.
If your camera allows you to shoot raw, that makes it much easier to get the WB right after the fact, so you do not have to worry about it while diving.
Enjoy!