When it comes to things involving earphones I'll usually have it on the lowest possible setting I can have it on where I can heard it. I don't know why but I've never liked the thought of someone being able to hear what I'm listening to, it makes me feel the same way as when someone is listening in on my conversation. The only times I'll turn it up are when I go jogging and idgaf because the people who can hear it can only hear for a split second anyway.
When it comes to speakers though I'll either have them on a retentively decent volume, so I can hear it clearly but so other people aren't bothered by it. Apart from when it's early in the morning and I crank it up to get back at my neighbours for keeping me up all night with their parties! :D