I'm not stranger to the gym. I've worked in gyms for a lot of my life as a strength coach, trainer or even a manager. There is some etiquette that goes hand in hand with sweating and moving weights around among other people in a semi-private space. One of the big ones right away is don't stink. It may come as some surprise to some but a shower before you go to the gym isn't a bad idea. I understand the logic of not showering beforehand, but trust me, you don't want to be the person that the trainer must awkwardly inform of your offensive odour that is leaving its mark in every area you wander. Same applies to your gym clothes. You will still have the same chances of lifting a new personal best if you run some water and Tide through the fabric once in awhile.
The next little etiquette point is returning the weights. Some people will show you just how tidy their house is when they go to the gym. They leave a trail all over the place indicating every bench and weight that they used. Listen Hercules, if you are strong enough to lift the weight onto the bar or move the 135lb dumbbells to the bench, then just put them back. If you really would like the rest of the gym to know what you lifted, ask someone to take your picture for your instagram.
That leads me to another point. The gym is a place to workout, not do the photo shoot for the next muscle and fitness magazine cover. Sure a quick selfie or even a video to check your form is acceptable, but ditch the modelling shoots. People are waiting for that piece of equipment so use it or lose it.
Dropping the weights is always a good one to touch on. It would be good practice to work out as quietly as you possibly can. Nothing is more impressive in the gym than the ninja beast who lifts heavy without a peep. Honestly, that person becomes legendary. The one that becomes infamous is the person that gives the senior citizen working out right beside them a heart attack with the boom of the iron hitting the floor. There are actually spots and platforms that are made for powerlifters which is completely acceptable, but the general area of the weight room is typically not for that; and almost never a good idea with dumbbells.
Don't be shy to ask for a spot. A spot is when you get someone to stand either in front, back, or beside you when you are lifting a weight that you may find a tad heavy. This is especially important when doing things that can pin you to the bench like a bench press for instance. The rookie that gets pinned usually doesn't have the strength to push the bar back up and now has it resting across the rib cage. There are only a few ways out of this predicament. One: A person comes to your rescue and helps get the bar up off of your chest; Two: You don't have collars on the bar and so tip the bar to one side causing an avalanche of weights to hit the floor only then to immediately feel an extreme river kayak motion jerk you to the opposite side of the bench (sometimes taking you with it) for the plate dump that happens there; or, Three: The wriggle. This is a good one where the individual then rolls the bar down their rib cage, over the stomach, grinding over the two prominent bones that some call their hips that are actually the front of the iliac crest, only to land across the top of the sensitive area of the pelvis. The individual then does a sit up of sorts, and attempts to stand up as the weights then roll down their legs scraping their shins on the way down to the floor or with any luck the person ends up capable of holding them and makes it to standing. Either option brings its own source of embarrassment and risk of ending up on social media.
Next, nobody wants to work out in your pool of sweat. Bring a towel and clean the gear you were using after you leave your residue all over the place. There are generally spray bottles available as well. Trust me, you are not Elvis. Women are not screaming and passing out to receive some sort of perspiration filled piece of cloth from you.
Lastly, the mirrors are for checking your form. They can also be used for a quick scan of the room, for safety purposes to ensure that nobody is behind you when you move, and even to check for torn body parts after getting the bar stuck on your chest. They are not for posing and flexing, nor are they for you to watch yourself walking through the gym with ILD (imaginary lat disease...a common occurrence where the individual perceives that their lats are so big that they cannot effectively let their arms hang by their side naturally and must walk around as if imaginary barrels are under their arms). If you truly are a competitive bodybuilder, then flex away...far away.. into another room. Nobody in the gym is a judge awarding you points today.
Yes, the gym is full of all different walks of life. The screamers, the grunters, the talkers, the gawkers, and the average Joe's. I bet it would be a fascinating place to study human behaviour. Just do your best to be a good person and respect others in the room and you will be fine.
Now back to my push ups...my gosh, all of these etiquette points would be twice as bad at a commercial gym.