Even though Ace has already mentioned it - GratefulDiver that was a good post and goes into more detail than what I've learnt through my OW.

Just one thing to add as well - if you're diving with a buddy, also plan what to do when you can't find each other (you shouldn't have gone too far from your buddy in the first place) - but what I'm getting at is that you should plan, for example, to only stay in the water for a few minutes then surface.
I hope you understand the point that I'm trying to put across - that it's not just about you, yourself to plan, but also for your buddy as well.

It's late.....i need sleep

Nite John-boy