Avoid task loading. Remember the K.I.S.S. principle, because stupid is what you'll be. If you've got a new and confusing camera housing, get familiar with it at shallow depths. And it's not just the picture you might screw up at 130 feet. You've got a diminished amount of attention to devote to everything, and if you concentrate almost all of it on f-stops, you won't have enough left for the little things like, say, how much air you have left. Diving with only one piece of new equipment at a time is always a good rule. Below 100 feet, it's a rule to live by.

Learn the 10 Ways To Outsmart Narcosis. Because at 100 feet, everybody gets narced.