ESSENTIAL TIP: Smile.

Seriously, is this the easiest thing in the world to do or what? Smiling at someone is the human way of saying "I'm not going to hit you with a brick" (usually) and "I want to connect, engage, talk." When you smile at someone you get attention, usually get reinforcement, and you open the door to the possibility of an emotional connection: at a minimum an acknowledging nod, and possibly a conversation. A smile won't always lead to a good interaction, but it's hard to have one without it.