One of the things I always recommend is to just practice talking to ANY stranger. You're going to be more nervous when you are trying to talk with someone you "care about" so it's good to have that practice in your history. Talk to the people in line. Talk to cashiers. You don't have to be pushy - just say hi, ask how they are in a friendly way. The more you get used to being "friendly" in general, the easier it will be to do it when you're faced with a girl you want to get to know better.
