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Be confident and outgoing. When a person realizes someone has those qualities, they find them easier to talk with and much more welcoming. Maybe if you are in junior high, shaking hands may not be the thing to do, but for anyone else, shake hands. If you are culturally aware that some groups do not touch the opposite sex, you may opt out of shaking hands, but in America, most people shake hands.
Don't be afraid to say hello to new people.
Smile and wave.