We haven't had too many people asking us to use our, but we've been intentional about inviting people over. I've seen some cute and some formal looking pool rules signs on pinterest, and I hope to get or make one for next year.
Our rules: No running. No diving/headfirst. No peeing in the water, no glass on the pool deck (we don't consume alcohol, and very rarely anything else that would be in glass bottles, so this is easy for us), and no kids in the pool without an adult supervising them. When we had a swim party where babies were invited, I specified no regular diapers, and that if they needed them, I would supply swim diapers.
Previous owners clearly had glass by the pool, as we keep finding broken bottles and other debris hiding in the rocks and glass by the pool. So another of our rules is: wear shoes on the grass.
I have no plans to let anyone swim in our pool without us there, but I could imagine an exception for trusted family members - none of whom live near enough to use our pool.
It's a liability concern, to me, to have people using our pool without us being there. In general, I don't trust other people to take care of my stuff the way I want it cared for. I personally have no problem saying NO to people. It's my stuff, my rules, and if you abuse it, you loose it.