I've been through stages, confidence very low and then very high. Probably about 3 times, although I currently couldn't care less which I think is the acceptance that stuff happens. Over those peaks and troughs I found that having a part time job when I was a student at college and university gave me something to feed on for conversation purposes with the other students (music mainly), and likewise the people I was working with at the job were planning to go or interested in further study and what life was like there. I didn't work at the student bar, but that would have been excellent - paid access to all comedy and music gigs and you get to know everyone there, some of my friends did and they loved it (although you have to clean up after everyone's gone). The high point was my 21st birthday when I had three groups of friends - the evenings out lasted two weeks
I found a job after my stint at university which had left me feeling very self conscious (not that I regret the experience). Shortly after I started there I was talking to a manager on a person to person basis, and somebody opened the door and all of a sudden I wasn't there because he had an operational issue to discuss, this unnerved me greatly and I was shaking until that person left. I wasn't angry, I just didn't understand what they were saying through lack of experience and suddenly felt exposed.
At that point in time I'd have been useless if it came to a presentation or social gatherings. I moved jobs eventually within the same organisation, which forced me to be a bit more talkative. I remained quiet but learnt my trade so to speak. Since then I've been promoted and I can't stop talking, when you have people and situations to manage you have to talk a lot (either to keep productivity and/or morale going).
The key to a good presentation is knowing your subject inside out, I remember being scared witless (and crap at presenting) about something I was shaky on (at uni), and being very relaxed on another presentation that was part of my day to day life (at work).
My shyness is almost history, because over time, and through being promoted I accumulated responsibility. A job gives you something to talk about, but it doesn't have to be boring. I'm not someone to throw a party, I'm busy and parties don't get organised by me (although parties are good). I don't let the day to day duties fill my conversation at work, it's about 50%. I like to think that people appreciate that, they seem to respond well.
The most effective social barrier breaker that I've found when it comes to conversations is humour/comedy. Recent shows like Carpoolers (Marm is very funny) / Dexter (dark humour) / SNL (and loads of others) and other stuff like the Simpsons/Family Guy can be good conversation fillers or even inspirational when it comes to one-liners, even if you're not quoting the show directly or you're speaking to someone who doesn't know the show. If it's appropriate to a situation then it's gonna work. Listening is a valuable skill too though. I used to feel that it was important to be directly involved in every conversation and felt left out sometimes, but it doesn't always work and you don't necessarily learn anything that way.