To know if a girl likes you, she will stare at you a lot and she will want to be next to you all the time. The girl will want to talk to you and try to defend you if someone tries to wrong you. Go tohttp://health.howstuffworks.com/relationships/tips/5-ways-you-can-tell-if-a-girl-likes-you.htm for more information.
Turns around to look at you, copies the way you're sitting/standing or something simliar to it, smiles at you, stumbles over her words when shes talking to you, always look at you and laugh at your jokes even if they arent funny, try to talk to you even if you know shes shy, blushes, when you catch her looking at you, shes looks away quickly... Yeah, thats all I can think of now. Thats what I do when I like a guy.