Last year on a dive trip I had the privilige of having dinner with Claude Hull, one of the original North Carolina wreck divers and the first US Divers dealer in North Carolina. Also at the table was a retired gentleman named Bud Daniels, who now is a mate on Olympus Dive Centers boat. Bud told me his first SCUBA lesson from Claude in the late 50's was;
1. Don't hold your breath.
2. Come up slow, no faster than your bubbles.
3. Bring my stuff back when you're done.
Bud told me he dove based on that till the early 80's.
I got a similar lesson in Greece from some EOD guys. It was basically:
-Don't go deeper than like 20 feet.
-When your ears hurt stop.
-When the regulator gets hard to breathe, swim up.
-Never hold your breath.
That pretty much carried me through until 2008 when I took an official diving course. You have to love not being mollycoddled.