Working out at a gym or a fitness center is good for you, but you share that space with other people. Even if you've learned how to use the equipment, you may not have learned how to be considerate of everyone else there to exercise too. This graphic breaks it all down nicely. 
They agree on everything, but the graphic includes a couple of extra tips worth mentioning (namely, not doing curls in the squat rack and not hoarding all of the weights just to yourself). You can see the whole thing below, courtesy of the folks at BestGymEquipment.co.uk.