How to meet a girl spontaneously?

I've never asked a girl out before because I've heard a lot that people meet each other randomly, or out of the blue, or spontaneously. i used to want a girlfriend about 7 years ago, but then I stopped looking and just focused on myself and hobbies and work without even thinking about girls. Sometimes when im out and about doing my own thing girls look at me, and i'd ignore them or something and not look or even talk to them because "stop looking". It has to be spontaneous right? serendipity. Not only that but im socially anxious to even talk to a girl because im worried she'll probably think im "looking" or "chasing". Seriously, what happens when im out and about and i see someone i like? I have no problem smiling at people or girls but I just ignore talking to them. Hence "Stop looking".
How to meet a girl spontaneously?
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