What pickup lines do you use to start a conversation with someone you are attracted to?
I pretty much always start out with a friendly greeting. I follow that up with a comment or question relating to where we are (club, amusement park, etc...). After that, just find out whether she is there with other people and what they are up to that evening. If the conversation to that point goes well, I then ask her/them if they want to join me/us and take it from there.
How do they typically respond?
With this approach, I have had success (I would say at least 2/3 of the time) and it might have to do with the genuine attempt to get to know them. Its important to display a calm and confident approach because its those brief moments in which a girl decides whether to deny you or is left intrigued by you and is wanting more.