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my opinion if you are walking oppsite of each other than start backward walking with her and looking up and down. it shows that you are checking her out, and she might interest you
I seriously hope you are kidding.... 
Anyways, next time stand tall, act confident, look her in the eyes, smile, and say "Hi" with a voice of confidence.
I would suggest forcing yourself to have more conversations with people to get used to talking to people. Make sure you really look into body language because that really conveys a lot to someone you are speaking to.