How to tell if you should approach someone in public?

I've grown more confident about the prospect of approaching a stranger in public and attempting the begin a conversation with them, but there's one thing that bothers me and that is when should/shouldn't you? I know basics like one word responses are bad, but what else? Would you find it annoying if you were on your phone or reading and someone started talking to you? Also are headphones an immediate no to begin talking? Also with one word responses, aren't they common for the type of questions you would start with? Like if I said "X book looks quite interesting, is it good?", Wouldn't they likely just respond with "Yes"?. Is there a way to make that more open or would someone who wants to talk just elaborate? Any help would be much appreciated thanks.