Like what should be expected at the range.
Safety is the most important consideration. That is the issue that everything hinges upon. For the most part however, this is not a range safety thread. It's more about the little (and not so little) things that shouldn't be done at a shooting range. Some are annoying, and others can be dangerous. Most of these examples have to deal with unsupervised ranges that are open to the general public instead of businesses and private ranges.
1) Make sure that the area forward of the firing line is clear before shooting. You would think that this would be a given for everyone but that's not always the case.
For example, a few of us were shooting skeet on an unsupervised public range a few years ago and had to call cease fire as we noticed two people headed downrange to pick up unbroken clays. No one ever asked for a cold range, or even gave a warning that they were headed forward of the firing line. As they appeared to be father and son it's interesting that stupidity can be hereditary.
Ah, then there were the people riding ATVs across one of the rifle ranges that I sometimes use. If you're a regular shooter you've seen similar things.
Pay attention to what's going on around you, and down range.
2) Watch where you point your weapon. Don't muzzle or sweep your fellow shooters. If it does happen, then you should apologize and make sure that it doesn't happen again. You just made a first impression on your peers, and it wasn't a good one. Don't say, "It wasn't loaded." That doesn't excuse sweeping other shooters. It only makes it more irritating.
3) Let the range go cold occasionally so that others can put up or change targets.
4) Don't ask for a cold range every 5 minutes so that you can check your targets, or paste them up. If you can't see your target with the naked eye then bring binoculars, or a spotting scope. Put up enough targets to ensure that you don't need to change them every few minutes.
5) Don't touch another shooter's gun, or gear without permission. I think that this should apply to RSOs as well.
6) Supervise your children. If they are too loud, too young or too immature to be on a range then do not bring them.
Keep an eye on your guests, non shooting friends, or family members.
7) Don't hover over other shooters.
8) Don't constantly offer unsolicited advice.
9) Keep the profanity to a minimum. Shooting is often a family activity.
10) Keep the BSing to a minimum unless another shooter actually expresses an interest in your stories. Sometimes people have time constraints, and really cannot listen to you talk about guns, politics or current events.
11) Stop annoying the female shooters. If they're behaving safely then leave them alone. Generally if they are there alone, they'll be the most safety conscious shooters on the range. They will ask if they need some help.
12) Bring the gear that you need. The public range where I sometimes shoot skeet is basically just an open field ringed by trees. You bring all of your own gear. It's not unusual to see people show up without earplugs, or other gear.
13) If possible try not to set up next to another shooter. If there's space available, then give people a little room.
14) If you're shooting a semi auto then be wary of where your brass is landing. If possible, you don't want to pepper the shooter next to with spent casings.
15) Shoot what is allowed on the range. Keep the handguns off of the rifle range, and the long guns off of the pistol range. This seems to mainly be a problem on the unsupervised public ranges.
16) Shoot at approved targets.
17) Shoot at the speed that is allowed on the range that you're using. Not every range allows rapid fire.
18) Pick up after yourself. It's unlikely that your mother will be there later to clean up after you.
Don't constantly get underfoot when picking up brass, if you reload ammo.
19) Don't tie up more than one shooting station. Spreading your gear across 2 or more stations is unnecessary, and rude.
20) Don't trash other people's guns and gear. Just because your Glock was forged in the fires of Mordor and quenched in unicorn tears doesn't mean that it's the perfect choice for everyone else. You may have picked a great gun, but it may not fit another person's needs.
It also worth mentioning that some people have more of a Hi Point budget than a HK lifestyle.
Don't ruin someones day and shooting experience by belittling what they bring to the range.
21) Leave the firearms unloaded, and with the action open when going downrange.
22) Don't expect total strangers to let you shoot their firearms, or loan you gear.
This post will probably be edited repeatedly, as I hear about other's pet peeves.