1. Chart topper always is “You are beautiful.” And while saying it shows that you really mean it. There are also many variations of this most popular flirting pick up line like “You are HOT”, ”You are Sexy”etc. But keep in mind most of the girls will get offended if you start telling them, how sexy they are in your first meeting. So always rely upon tried and tested “You are beautiful” while looking directly into her eyes.
2. Compliments: None of the girls can resist compliments even from the creepiest males. Every girl secretly will do anything for getting complimented. Compliment her for any and every thing. E.g. Compliment her cooking, Compliment her sense of Humor, Compliment her selection of color etc. Use many “I like… “ lines e.g. “I like your bracelet, can I see it?” Make sure your compliment should not be too boastful, too cheeky or too vulgar.
3. Every girl despite hating in-laws always wants to be appreciated by all people in the world. So something like “I want you to take home and meet my family” may do wanders.
4. “My life long ambition is to visit Paris (or whatever – try to pick a place that is in her wish list). Will you travel with me to Paris, if we get a chance”. With this line you are fulfilling her life long wish without really showing that it is her wish, not your wish. Who won’t like it?
5. “You complete me” – These are the lines from one of my most favorite one liner movie Jerry Maguire. These lines not only compliment a girl on physical beauty side, but these compliment on her overall personality.
However in summary always keep in mind a girl always likes to hear "COMPLIMENTS, COMPLIMENTS and COMPLIMENTS". However while passing a compliment, don't overdo it. Also make sure that compliment should look sincere.