Start talking to everyone you see. Men, women, kids. Nothing big, nothing heavy.
Just things like -
- Nice weather we're having
- Does this bus stop at ___?
- Is your dog friendly?
- Do you know any good Chinese restaurants around here?
Obviously, tailor it to the circumstances and make up any number of other light tidbits of conversation. These are meant to be short and sweet; you're not proposing marriage to these people. And with children, don't talk to them unless you're also in the presence of their parents.
The idea here is to get used to breaking the ice and talking to your fellow humans. This doesn't cure all forms of shyness, of course, but it does help you to improve at striking up conversations.