Watch for signs of flirting. If she's flirting, she may be difficult to read. Flirtatious girls may flirt with guys who they consider to be just friends, and it can be misconstrued as a crush. Because most girls do not want to be obvious, the flirtatious ones might flirt with you a little bit less or they might flirt with you even more. Either way, don't "flirt around". Do not flirt with other girls. If she ever sees you putting your arm around another girl or sees another girl hug you, she may jump to conclusions and assume she doesn't mean anything to you.
Notice if she touches you more often than what friends do (she's constantly trying to touch your hand or something). If she finds excuses to do so, then you're probably on the right track. But conversely, don't assume that just because she isn't touching you that she doesn't like you. She may be too nervous of you to touch you yet. Break the touch barrier yourself.
Observe how she looks at you. If she like you, she will either hold it for a long time or pull away immediately. Either of these could mean that she likes you. If she pulls away quickly, it means she is nervous but she still likes you - which means that you should probably make the first move. If she holds the stare, then she is confident and she may make the first move. If you happen to glance at the girl and you see her staring back at you, then this means that she likes you, although she may quickly dart her head in a different direction. Look for her eyes to light up when she sees you or hears your name.
Look at her friends. If you see most of her friends glancing back at you and smiling or giggling, this means that she is telling her friends about you. If her friends are loud and immature, you'll hear "(your name), (her name) likes you!" Her friends might be making it up, however, just to tease her. When she is having a conversation with her friends, and you come over, she might stop talking all of a sudden. This likely means you were the subject of the recently ended conversation. If she likes you and she told her friends about you, they might come up to you and start a random conversation about things such as: Who would you rather date?, Who do you like better?, Who is the hottest?, and such. If they name a list of about 3 people and her name is in the list, she probably told her friends about you and they're trying to search for clues to see how you feel about her.
Personal Questions If she constantly asks about your status with girls and asks your preference in types of girls, then she is likely fishing to see if she might meet your interests.
Once you've figured whether or not she likes you or not, affects what you do next. Either move on if she doesn't (it can be hard but its probably best) or keep contact and start making your move if she likes you!