Being that this is in the reining section, I am going to make the assumption (dangerous, I know....) that we are talking about REINING shows. They are definitely unique.
The common thread tho seems to be paying attention! To your horse as well as those around you. Use common sense (which is not so common, unfortunately) and courtesy!
I find reining warm ups really intimidating.....I am pretty new to them, and thankfully have a horse who does best by himself, and I try to warm him up in a quieter place, rather than in the show arena with 50 people all running and fencing their horses all at once. However, at least for the most part, they are all courteous enough to all go in the same direction at once during the fencing, and are smart enough to do their circles so that they are not coming head on toward each other. Which, by the way is NOT what I found at H/J shows where it is literally every man for himself and you had to be looking in 50 directions all at once! The reining people I have encountered are also all very nice and supportive-they don't seem to be as "cut throat" as what I was used to in the english world. I think NRHAreiners attitude of having fun may be more common amongst them.
I also go to have fun. I will not sweat the small stuff. I used to, but not anymore. Just leave me alone and let me do my thing. If you choose to be miserable and let everything bother you-please just do it away from me. I pay too much $$ to not have fun doing it. When it becomes work, or I stop enjoying it, I will stay home.
Rude kids with parents who pay no attention to them are an issue everywhere, not just at shows. If they are around MY horse, I will speak to them myself. If they have a problem with that and run and tell mommy, so be it. I will be glad to talk to her too!
My kids will gladly tell you-do not mess with me.