As far as it goes for me, confidence is the thing - as parent says. I had big problems a few years ago, being picked on at school and so on. My response to this was becoming quiet (I was less picked on if I just didn't say anything) and invisible. This still haunts me, several years laters. I've got loads of friends and the best girlfriend I can imagine - but still I'm having trouble being open and "loud" in front of unknown people. I guess I've never learnt the ability to start conversations with people.
The last years I've gotten better at this, luckily. This has a lot to do with my girlfriend, since she is pretty much the oppsite of what I used to be. She helped me increase my confidence in myself so much. I guess my point is that sometimes you need to have someone to help you get towards your point. This can be a girl/boyfriend, family, friends or someone you meet at the Internet (like this forum). People who've dealt with the same thing can be extremely usefull.
I'm no big fan of things like forcing yourself to doing this and that. If it feels unatural I can never do it properly. But by doing things with (the help of) a good friend the steps can (and probably will) become much smaller.