I mean, you don't want somebody to start liking you for the way you think THEY want you to act or talk or dress. Why would you want somebody to like you when you're not even being yourself?
Secondly, don't be shy! Just go up and talk to that boy/girl. Confidence is key. Strike up a conversation! Start it with something like, "I see you're wearing a Hit The Lights [or whatever band/sport's team, etc] shirt, are they your favorite?" Or, something like, "So I know we've never talked before, but you seem like a really cool person..."
So be yourself, and show that you're comfortable being just that. Be comfortable in your own skin, and chances are, you'll impress everybody.
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