We are lucky to have sand arenas in 2 parks (you have to be a member in one, and free for everyone in other). I always pick up after my horse, if I use barrels or jumps I put them back, and I lock the gate when I'm leaving. I think that's pretty much it. Also sometime even it's on first-come-first-serve basis you have to share it with other people, so I just try to stay off their way as much as possible (arenas are very big, so it's not that big of a deal).
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."