How do you tell if a girl likes you but you don't know for sure?

you can tell her a joke and see if she laughs really hard or tries to hide it and pretend your stupid... try making eye contact with her, if she looks away fast or she may try to hold it (depends on the girl) see what she does when you talk to a different girl, and see if she gets jealous by starring....go straight up to her and ask her who she likes and see how she responds, if she said "no one", "its a secret" than she may like you... but dont jump to conclusions