Just show unashamed interest in other people. Look for things you have in common with other people. Maybe strike up friendships with people in your favorite electives or groups, like band class, a robotics club, etc.? A sure way to make friends is to join groups like that. But most of all, like I said, just don't be nervous as if you have anything to apologize for because you've approached a stranger. People aren't all that bad. And if they are all that bad just because someone approached them, shrug it off and move on. Of course it's harder than I'm making it sound to not feel dejected, to keep good expectations, but this is a life skill that we just have to learn however hard it may be to learn.
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There is no wealth like knowledge, no poverty like ignorance.
Nahj ul-Balāgha by Ali bin Abu-Talib