practice. It took me years to get out of my shell, and I still go back every once and a while. Its human. its who you are. As I have said in other threads regarding shyness, my experience breaking it involved putting myself in positions where I couldn't be shy. After a while, you realize the fear is unfounded and you get confident exerting yourself. Sports reffing was a great way to accelerate this. They even teach you how to not talk like a sissy.
Alcohol does this to everyone which is why a good number of folks drink. Heck, I do too! All it does is artificially make you not care what other people think. If you can achieve this w/ out assistance, than your shyness should abate.