The best way to get a girl interested is to tease her with your attention. When you're talking to her, focus all your attention on her, talk only to her, and treat her like she is the only thing you care about.
However, suddenly draw your attention back and ignore her. Go to another room, talk to other people, get involved in a game. Later, return to the girl and once again focus all of your attention on her.
As a girl, I can tell you this works really really well.
By giving the girl all your attention she feels really special and she feels really good to be around you. Then, when you draw your attention away, it makes her miss you, which makes her want to be around you even more. It also makes her think you're a cool guy by being really social and fun, instead of some needy loser who only wants to be around her.
When you come back, she'll be really happy that you came back and she'll really appreciate your attention. Once again, focus all of your attention on her, and then suddenly have to leave again. And then at the end of the night tell her how much you liked talking to her, and that you'd really like to see her again sometime.
Should work like a charm.