Talk to her, sit by her in class. Ask what they did yesterday, and make the girl laugh as much as possible. Just smile at each other. Sadly I'm fifteen and never had a girlfriend :(
sorry im not a boy but the answer is
they act STUPID
i can't see her in the eyes in a minute.. i always talk to her..
Me well im 14 and a guy and when i like a girl im smooth, like barbed wire. Anyways I shy so i dont say much but i guess i try to be with er more you know just me and her because well i like her . I try to make her luagh (but usually fail) and i laugh at her jokes even if they arent that funny oh and its not that make myself laugh its a genuin laugh.