What to do about the MYSTERY GIRL?

This may sound lame, but I was out at a club with my sister and her mates the other weekend, and before we were about to leave my eye caught on of her (my sister) friends, friends if that makes any sense. She was possibly the most amazing girl I have ever seen, and this may sound stalker-ish, which im completely not, but I really want to see more of her shes that breathtaking. what should i do in terms of what to do next and how should i go about talking to her etc! thanks!