It really doesn't take that much to be a friend. Haha, that's an odd thing to hear from me. I'm terribly shy. But occasionally I'll meet a person and I'll just know that we'll be friends, and we might become friends. You need to smile and wave when you see them, show genuine interest, invite them to things, make them feel included, and offer to go with them places or help them. You should ask how their day is going and wish them luck with their events. Even if you don't have much in common, if you display loyalty, their trust is yours.
:)