Know what you're breathing! Be confident and ensured that you have right mix for your dive. The Scuba Doctor is proud to be a supplier of the Divesoft range of He/O2 Trimix and Nitrox gas analysers, plus the Analox range of Nitrox and Trimix analyzers. These dive gas analysis units are simply the best available.
Trust No One
Get an analyser. Learn how to use it properly. Calibrate it before every use. The only person who should be analysing your cylinders is you. The only analyser you should use is yours.
Clearly label anything that isn't air. If the MOD is less than the maximum possible depth of the dive (think deco cylinders), make sure the MOD stands out where not only you can see it, so can your buddies. Make it obvious to everyone if you are using the wrong cylinder at the wrong depth.
Consider putting a small piece of tape on each second stage, just in front of the mouthpiece, that has the MOD for the cylinder it is attached to. (This is in addition to the standard cylinder markings.) Any little thing that may save your life helps.