We all love Col. Cooper's Four Rules of Gun Safety and I'm certainly not trying to improve on them in something as trivial as God Damned blog post.
However, I've been observing and shooters at firing ranges long enough to notice a few things that might make your range trip safer or more pleasant.
1) If you pick up a live, unfired round from the ground and intend to shoot it out of your firearm, make sure its the right caliber.
Picking up rounds off the ground with the intention of shooting them is almost always a bad idea, but I can imagine a couple cases where it might be necessary -- eg, you dump your 100 round value pack of Winchester White Box on the ground, and you'd rather not kiss 30 bucks good bye. Just make sure that they are your rounds you are picking up. A .40SW looks a little bit like a .45ACP if you aren't paying attention, and in some .45s, you can chamber it and fire it. But as the round doesn't fill the chamber, you can expect some unpleasant consequences.
2) Put your range bag where nobody will trip on it. Especially you.
This shouldn't require any explanation. Tripping over your range bag while holding a loaded firearm is a Bad Thing. Having someone else drop their $2000, tricked-out AR on concrete cause you left your bag in a dumb place will not cause them to love you, even if they should be watching where they are going.
3) When shooting someone else's firearm for the first time, make sure you know how it operates, where the safety is, and -- this is very important -- how much it will recoil.
Just this weekend at the range, I saw a man shoot his buddy's very modern muzzle-loader. This guy had obviously never fired this particular shootin' iron before, and when it went off, it produced the usual thunderclap and huge cloud of smoke and an unexpected yelp of pain from the shooter. The recoil had thrown the scope back into his head, and put a deep inch-long cut right above his eye. It bled like crazy, and the family day at the range ended rather quickly with a trip to the emergency room.
4) If you need to pick something up off the ground, put your gun down first.
This is more of a guideline than a rule, I guess. There are probably situations where it would be perfectly safe to bend down, rifle or pistol in hand and grab something off the ground. But if you're going after an en-bloc clip that your Garand just ejected (ping!) 8 feet to the right, you may muzzle-sweep someone else as your 1-handed grip on a 9.5 lb rifle is revealed to be too weak and the dangerous end goes wobbling around. (In a real live self defense emergency, don't put your gun down without a very good reason. Remember, these are RANGE rules.)
5) If you drop your gun, don't try to catch it. Also: if you drop something else while holding your gun, don't try to catch that either.
6) Although not required, if you think that you might eject hot brass (or maybe an en-bloc clip) onto your neighbor, it's polite to let them know. This means you should be aware of how your firearm ejects, and what's around you when you are shooting. Consider it a situational awareness drill.
Little kids or new shooters are particularly deserving of a friendly heads up - a rattled new shooter might turn sideways and inadvertently injure or kill someone with an ND. I've never read any accounts of this happening, but it costs nothing to be friendly. There is not a corollary to this. If you get hit by hot brass, don't be a whiny little bitch. It's a shooting range. Put on a hat or go stand somewhere else.
7) If shooting your hand loads causes your revolver to Ka-Boom (TM), showering other shooters with bits and pieces, instead of packing your stuff up and departing without saying a word, apologize to the folks around you.
Yes, this really happened to my co-blogger. He was the shower-ee, not the shooter.
Any other suggestions? Please post them in the comments.