One of the best "pickup" lines is saying, "Hello". Generally if the person is interested in you, then this will allow a conversation to start and the rest to follow.
Other times, you may have to be more persuasive. Note: this should not be anything sinister. If a person shows an obvious distaste for you, it is best to move on and leave them alone.
If the person is just bored and flicking people off whilst barely looking, perhaps there is a chance. She may already have a partner, not be in the mood or whatever. Depending on the reason, you may be able to turn her around or shake her out of it with a witty comment or something.
A bit of preparation can help with your subsequent conversation. If you are making the approach, look around for things you can comment on. Note, we are talking witty, not weak pickup lines.
Just don't take it too far and know when to move on.