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"How are you?" feels a little too familiar for someone you're meeting for the first time, and "How do you do?" feels quite old-fashioned to me. It really depends on the circumstances under which you are meeting, so I think that if you are meeting for a specific purpose (work, etc.) you would start with conversation related to that, and if it's someone you're meeting for the first time out and about or through a friend, you might start with a comment on the location at which you are meeting or something generic like that. This is my perspective from the US. :)