How to be more approachable?

Never ever in my entire life has a guy approached me (ok, there were two exceptions: a tourist, who just wanted some fun and a man in his sixties). I am wondering what is wrong with me? I'd say that I'm an average looking girl with an average expectations. The truth is that I'm not a party type of person, but I guess there are plenty of guys who prefer reading or training to partying. I wish I could be more approachable. What should I do?
How to be more approachable?
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