actually, i think as long as the guy is "not revolting" in
appearance, and comes up to her and acts "normal and friendly", the
girl will probably be pretty flattered by the attention, and
respond favourably.
don't "over-plan" it inside your head. what you say will never be
the same as what you rehearse in your mind!!! 
open a converation with the right person. don't engage anyone who
looks busy, in a bad mood, waiting for a bf, etc. another good
idea, if you're with a group of guy friends, is to join another
group of girls sitting at the other table in the coffee shop, or
something like that. try to look for a group that are in a good
mood, happily chatting, etc. Have one guy just approach them,
smile, and ask if they mind if he and his friends join them. Be
nice and friendly; it's unlikely they will turn you away.
