Things I wish I'd been told before my OW class (and things I've learned in the short time since):
1) Your first couple of breaths underwater in the pool will probably feel...odd, for lack of a better word. That's normal. It takes a little time to adjust your mind.
2) Mask skills (including remove and replace) are no big deal whatsoever. I got all psyched out for nothing.
3) Buoyancy control is CRITICAL. Work hard at getting yourself neutral. It's important.
4) Follow the same routine in setting up and checking your gear, every time. Don't skip steps. If you aren't comfortable with the results of a check, stop. Correct the problem or ask your instructor.
5) If you run into a problem underwater, stop. Breathe. Think. As long as you have adequate breathing gas, all else is secondary.
6) Slow is smooth. Smooth is fast.
And lastly...carry a plastic grocery bag in your kit. Use it to slide your feet into your wetsuit. And putting on a damp wetsuit (or a dry wetsuit on a damp body) sucks. ;-)
-Mark
