First, I think you need to be clear on whether you are a “ring steward” or “equipment checker” – they are different, and at a recognized show, you are not allowed to do both jobs at once. It sounds like you are talking about equipment checker.
The equipment checker needs to check at least 1/3 of the horses in each class. But the TD can instruct you to do more, or to do every horse if he-she wants. There in a handy guide on-line that tells you what bits are legal, and shows a diagram of how to check the tightness of the noseband. You need to put on two fresh gloved for each horse. You really do need to get your finger far enough into the horses mouth that you can feel whether there is a roller, or any sort of ridge, moveable parts, dangling parts, etc. that might be illegal. You will almost never find anything illegal. Most competitors just use a plain single or double jointed snaffle – or if they want to use anyting unusual they have usually checked in advance that it is legal. Still, you really do have to check. Also, the show should provide you with a way to measure whips. This will not be a tape measure. It will be some sort of markings or tape on a nearby fence, wall, post, etc. to let you know what the max length is. You also need to check spurs. Again, pretty much everyone knows the rules and has legal spurs. The one exception is that sometimes relative beginners wearing prince of wales-type spurs just didn’t notice that they are slightly tilted and will accidently put them on so that they are tilted up instead of down. If you see something like that, you need to let the TD know, but he/she will usually just educate the competitor and not make a big deal out of it.
If you see anything that looks like blood or welts or injury anyhere on the horse, basically, you need to let the TD know right away. If the TD is going to be there in a couple of seconds, then you probably just want to wait for him/her. If it might take a couple minutes, then you are the first person on the scene, and it is your resposibility to blot the blood with a kleanex or a white glove. Just lightly press the kleanex onto the area, and pull away once. Don’t rub or re-check. Then note whether there is blood on the kleenex/glove and save it for the TD to see. That first check you do is the one that counts, because bleeding can start or stop, old scabs can come off and re-bleed, etc.
Also remember that “blood” does not equal “abuse”. Your job is to determine whether there is blood anywhere on the horse. Sometimes it is something completely innoccuous, or somthing not done by the rider - i.e. and over-reach or interfereing injury, a sore from rubbing in the trailer, etc. If there is blood, then the TD will decide whether it means that the horse needs to be eliminated or if it is “innoccuous.”
Ring steward on the other hand keeps an eye on the warmup ring. The thing that you absolutely have to do is to be available in case of an emergency - i.e. to call the medic, or to ask other riders to stop, or to do whatever is needed to preserve safety. The other thing you should do is to keep track of who is in the ring, who is going next, tell riders when to move toward the ring, and be available to answer questions about when they go. You need to be courteous and to do your best to help them. However, it is ther RIDER’s responsibility, not yours, to make sure that they are on time. You are simply one resource to help them. Lastly, if you see anything going on in the warm-up ring that might be unsafe or abusive, you need to call the TD, and you need to keep your eye on it so that you can give the TD a good description. Again, this is very rare. You should be aware that it is part of your job, but don’t worry too much about having to turn someone in or get them in trouble. I have been ring steward at many shows, and there has never been anyone formally reported for abuse or poor sportsmanship.
