It's amazing how much your demeanor matters. You can't just go through the motions when it comes to socializing--if your heart isn't in it, it comes through in every single microgesture, and people see through your perfunctory patterns instantly. They won't even know they're doing it; they just won't respond positively to you, and it'll be a lost cause.
Assuming the neighborhood is safe, if you want a kick-ass warmup say hi with a smile to 50 people. The first thirty or forty or so (e.g. why am I trying) will suck but once you hit the social warmup zone people will start smiling back and responding and you will be ready to mingle.
> As for social fearfulness, it should be eked away at whenever possible.
I have friends who are natural at meeting anyone, anywhere. Unfortunately it all comes down to how committed you are to meeting someone. The difference between hovering vs. a weakish handshake vs dragging a chair across half the floor rather loudly to sit with a bunch of people who you'd like to meet.