I've said this before and I will say it again and again, just because you are an avid gym go-er it does not make you an expert.
This will be Rule #1:
Please do NOT give unsolicited advice.
Many people, who are both new and old to the gym, are probably doing something wrong. It is not your place to correct them even if you think you know how to. Unless you are a trainer and work at the gym you are training at, it is not your place. If you feel compelled to correct someone's form or change their exercise, point it out to the trainer, that is what they went to school for and that is what they are being paid to do, help out.
Please PUT YOUR EQUIPMENT BACK!
I know that you are probably planning on doing 3 sets of 15 with the 6kg weights, but there may be other people waiting to use the same weight and can probably share nicely with you. However, if you insist on keeping them with you until you are done with your sets, put the weightds back where you got them from. PLEASE. True, the trainer is there to tidy up the place and make sure things are in order, but is it really that hard to put things back where you took them from? Wasn't it nice to be able to find the right weight where you first looked for it? Pay it forward. Thank you.
Wipe down your equipment before and after you have used it.
Although most people come to the gym to improve their health, the gym is one of the more germ-infested places you can go and contracting some infection is inevitable. To minimize exposure, be sure to use the anti-bacterial sprays on the surfaces and handles of equipment and lay down a towel before you sit or lie down on a bench or mat. Your body will thank you and you will be setting a great example for other gym go-ers.
Don't walk too close to someone exercising.
Most exercisers are concentrating on the exercise at hand and not focused on making sure they don't hit passerby. Walking too close to someone in the middle of an exercise can throw them off balance and can be perpetually dangerous for both you and them. Give them the space you would want to get.
No shoes, no shirt?...No service. Exactly.
Now I am all for the barefoot movement. If you are alone in your own gym and have control of what you are doing, or are in a class that requires you to take off your shoes, take off your shoes and go about your business. If you plan on doing heavy Olympic style lifts, buy shoes that mimic barefoot training and keep them on. Shirts on the other hand are another story. No one wants to see your newly acquired beach-bod especially if it entails sweating all over the gym without cleaning up after yourself. For women it can be a bit easier, so ladies, if you are comfortable enough to workout only in a sports bra, 1. Good on you., 2. Make sure you use your towel as a barrier between your sweaty back and the mats.
Both being shirtless and shoe-less can lead to unnecessary germ-spreading/catching and can be disrespectful to those around you.
Now I hope that you do make it your New Year's Resolution to get fit and be healthy. It's not a fad, it's a way of life and it takes some time to make it yours but I promise you will not regret sticking with!
May this year be one of accomplishing things you thought weren't probable, since nothing is impossible if you really want it.
Happy New Year!