Standard etiquette in a men's locker shower area is to wear shower shoes, get in and out quickly, and dry off before exiting the shower area. It's good etiquette for a man to clean up after himself when using any part of the locker room, including the shower area.
Shower shoes protect a man from skin infections, such as athlete's foot, and also shows other people that he is concerned about being hygienic. Showering quickly is important when it's busy, so those who are waiting to shower can do so and leave. A man should dry off before leaving the shower area to avoid getting puddles of water on the floor. These can pose a hazard, due to germs and the possibility of people slipping and falling.
Although some men leave a towel on the door handle to indicate that they're reserving it, no one has the right to save a shower. A man should keep his things in his current area and clean up before he leaves. After using a towel, he should put it in the hamper instead of leaving it out.
General locker room etiquette dictates that everyone should bring a lock. If a locker is left unlocked, items can be stolen more easily. Also, another man may open the locker by mistake, creating an awkward situation. Cell phone use should be kept to a minimum to avoid the idea that a man is taking pictures of others.