I mostly shot WA with artificial lights and deep so my habits could be very different if you shot shallow.
I shot completely manual: shutter speed twice the frame rate. i.e. 1/50 for 24/25p or 1/100 1/120 for 50/60p. I try to stay at least at F5.6 even better F8 to minimize soft corners. Of course if you are shooting shallow in tropical waters even ISO 100 could force you to use F11 or more. In this case I suggest a ND filter to work always in the best F range.
I ALWAYS try to stay in the hyperfocal range so I set my Panasonic GH3/GH2 to use the AF Lock feature. I focus on a medium range object (based on shot subject) locking the focus and then I start shooting.
Regarding ISO setting I rely on my experience on similar dive conditions. In my case most of the times I start with ISO 800 or 1000. As I said I mostly shot at depth of 60/70m or even more so ISO 800 is the bare minimum even with my two Keldan Luna 8. I can lower ISO for close WA shots where my lights completely fill the subject.
An evergreen topic is the WB settings. You will find endless threads on it. For my kind of dives I rely on auto WB but, again, your mileage may vary on your DSRL and if you shoot shallow or with ambient light.
EDIT: I find this to be a very valuable tool to understand how to get hyperfocal settings for your configuration: http://www.dofmaster.com/dofjs.html
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