No girl wants to hear a line to pick them up or anything that is not true. Therefore, choosing their words carefully will always help. You always want to be honest. Choose something that you like about the girl and make a nice comment to her. Always have good eye contact with her. It is helpful to smile a lot. Some people will tease others but you must be careful when teasing because the girl may take offense to it.
If this is the first time you have met this girl, you should not touch her, but smile a lot and give a lot of good eye contact. The words you say to her are important because they should be playful, but true.