When I was in high school, I swear I would do this without even thinking about it.
I would sit 2-3 chairs away from the "target" and I would listen to conversations that she would have for 1-4 days.
Then I would sit next to her on the 5th day and strike a conversation that had to do with her general likes etc, then when they would ask about me I would flip it around and look right into them and tell them what they really like, and what they really wish they could do.
Then stop talking to her altogether, if she's interested(They usually are) they will come right to you and start a conversation.
Hook, line, sinker.