What types of precautions are necessary for SCUBA divers? There is a whole course called Basic Open Water that is devoted to that. But here are some general, and by no means exhaustive list of things to ponder.
SCUBA is, if done properly is a relatively safe adventure sport. That said, stuff happens.
Proper Training is of course the first precaution.
Next comes Proper execution and retention of that training.
Never ever close your airway or otherwise restrict air from escaping from your lungs.
Dive stone cold sober (aka not under any influence of any kind, legal or otherwise) always.
Hydrate, hydrate, hydrate with H20, not cokes, tea, beer, just water.
Be physically fit
Be well rested
Do not Fly or change altitude by more than a few hundred fee immediately following diving. Follow the no fly guidelines. Note, I can personally attest that 1400 feet elevation hurts if you have any bubbles in your body, 200 feet elevation feels much better. If you have to drive over tall hills (not mountain passes hills), do so after having first enjoyed some food and leisurely conversation with your dive buddies for a few hours after the dive.
The dive is not over when you surface. The dive is not over when you are on dry land. The dive is not over for several hours after you have surfaced and fully off gassed your nitrogen load.
Enjoying a meal and leisurely conversation with fellow divers after a dive is not just sociable, it is part of the dive. It is where your dive buddy talks to you and listens for slurred speech (no you should not be getting hammered at this point), and mental confusion (OK so in my case that may be a tough call) and looks for drooping face muscles, loss of muscle control and other DCI symptoms, just as you are watching them.
Do not dive with congestion
Evaluate conditions and make the conservative safe decision.
Watch your gages, do not cut it close on air or NDL.
Watch your dive buddy and be able to thouch them always.
Do not dive with fools or daredevils. Select your divebuddy carefully and wisely.
There is a whole long list of stuff, that is why they have all those pesky classes. The above list is not close to all of them.