Commenting on the situation at hand is always good for starting conversations. Shared anxieties, like asking someone "I've never done this meetup kind of thing before, are you new too?" or telling them that you're a little nervous but the other person looks like they're a fun person works. I wouldn't use any sort of canned opening line or something, just go off what you have at the moment. The best conversations are when you start with something for a person to hook on to. The wide open "how are you" or "what do you do" are both so boring so as to translate that boringness to you. Asking someone if they've seen the new art exhibit at the local museum is nice, and if they say no, you can say something like "neither have I, you look like someone who has a lot of savoir faire though" and just lead into a conversation about art or fine things. When in absolutely dire straits, talk about travel with people. Everyone loves to talk about traveling places or their dream vacation!
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