Imagine that you are chatting with your friend, not with a beautiful girl. This will help you to get rid of some of unease. Try to act natural, be yourself.
Communicate on topics that interest you both. No need to tell the girl about the latest football match or to talk about the problems in your car's engine if the girl is not versed in these topics. If you see that your interlocutor looks away, picking at clothes or pen in hand, ceases to serve replicas, that means the topic of conversation is uninteresting to her. Try to find something in common between you.
Be gallant. Help the girl to wear clothes, open doors for her, give a hand when you exit. Any representative of the fairer sex will appreciate it. If you see that girl you, put your Affairs and help her. And let it be little things, but they will prove your concern for her.
Compliment. A rare woman can resist a knight praising her. Don't be afraid to overdo it, nice words never too much. Let your compliments be a bit awkward, and it's not too smooth. Still it would be nice, because your words come from the soul.
Never lie. The fairer sex thanks to his intuition can understand a lie very quickly. Even if there's no evidence she knew about the cheating and, most likely, will stop communication with you.
If you have serious feelings, give her cute gifts and bouquets of flowers. Rare girl can resist a nice guy who is having her attentions.
Show her your wit and erudition. Many women love intelligent and well-read guys. Therefore, the company try to Shine with intelligence, even in small things.
Don't lose confidence. A girl can't understand what you are timid upon meeting her. Smile is the best way to show your attitude.