Steer clear of all clever-sounding, sexually driven pick-up lines.
Chances are she's heard them all before, and even if she hasn't, she likely doesn't want to.
Start with a basic introduction.
It doesn't need to be anything fancy or over the top. Make eye contact and when you're in close proximity, simply introduce yourself as you would to any new acquaintance or friend, and hopefully she'll respond.
Ask her something about herself.
It's an easy way to start a conversation while giving you insight into her person and personality. You'll soon be able to gauge her reaction and interest in the conversation. If she's interested, she'll continue to take part by asking you questions as well. Let the conversation take its course naturally.
Relax and calm yourself by positive reinforcement, remembering your great qualities, and not putting too much pressure on yourself.
Treat the conversation as if you're meeting someone for the first time, but don't make it all all-or-nothing evaluation of your skills with women.
Listen to her.
Don't just hear what she is saying, but truly follow along and take interest in what she is sharing with you. Short comments such as "right", "sure", "I see" and "yes" show her you're following her words. Continuing the conversation by including a detail or subject she just mentioned is another way to show her respect for your conversation with each other.
Read her body language.
Does she make eye contact? Smile? Lean toward you? Feel comfortable. These are good signs. If her arms or folded, she looks away or looks distracted, or seems hesitant, she may not be comfortable even if her words are polite.
Share your interest in talking with her again by simply sharing that thought or asking for her phone number.
If you feel comfortable doing so, you're likely getting a positive vibe that encourages you to do so. If you do get her phone number, call her.