Everyone has the right to be in the gym regardless of skill level.
Rerack your weights.
Plates go on racks with the lightest on top and heaviest on bottom. 45s should be the lowest rung. This is a safety issue so people aren't taking 45s off above their heads.
When you take dumbbells off the rack, step away from the rack don't stand infront of it.
Don't stare at people. looking around is okay just don't stand there staring at someone.
Bring flip-flops for the gym showers to prevent spread of foot conditions.
Don't interrupt someone mid-set. Wait for them to finish before getting their attention.
Don't give unsolicited advice.
Don't go to the gym when you're sick.
Don't deadlift in the squat rack. You can take a free bar to a free space on the floor.
Don't use a camera in the change room if someone else is in there.
Wipe down your station after use.
No one wants to hear you shouting with every rep.
Don't drop weights (unless it's to bail on a lift for safety). It damages gym equipment,