Don't feed the fish. The wrong diet can make them sick or even cause death.
Don't throw anything into the pond. This should be obvious. Parents be parents-watch your kids!
Don't stand on the edge of the pond or climb on rocks. All edges are not mortared. They can shift and some are wet and become slippery. Stay on the main walkways.
Do ask questions. Owners will be happy to share what they know about ponds, plants and fish.
Do take lots of pictures. This is your opportunity, take advantage of it.