You've got some great answers here, and I'm going to add one more.
I used to be pathologically shy. Zero eye contact, dressed to be ignored, intermittent hygiene, damn near permanent stutter, the works.
Two things changed everything:
1. I moved 3000 miles away from anyone who knew me. Any way that I presented myself to my new community would be how they thought of me. I made a conscious decision to not blow that opportunity.
2. Brute force: it was HORRIBLE. I explain: I gave myself a challenge. I had 2 weeks to change my behavior. I didn't have to change my mindset, just my behavior. I went to the least threatening place (college science lab) at the least threatening time (4pm) to deliberately *give a compliment* to the least-threatening person I could find(older secretary).
Result: My hands were sweating, my knees shaking. I asked for directions to an office I knew was on the wrong floor, and as I went to leave, said, 'hey, that dress is a beautiful color on you'. Then I threw up in the bathroom.
And then I repeated it, in some form, every day, for 2 weeks. And it got me over the worst of the shyness. I started looking people in the eye, I bathed on the regular, got newer clothes, and talked slower to overcome the stutter.
You're probably nowhere near as shy as I was. The 2-week challenge will probably work great! Every day, find a stranger, and compliment them. Seriously, if I can get past it, you can.
Now? I may have gone too far in the opposite direction. YMMV