Good advice here so far... take heed.
I'll follow it up by adding to the "ASK QUESTIONS" line. To me, there is nothing more crucial for sincere, substantial social interaction than to simply ask meaningful questions, and to really listen to the responses, and then respond in kind. Don't just mirror what the other person asked you first; give it a spin, or quote something they said to you and ask them to expand on that. That is attentive listening, and it shows the other person that you are very keen on what they have to say, and they're more likely to feel comfortable opening up to you and asking you questions as well. The problem with some people (not saying this is you, but it could be) is that they act like a brick wall and expect the other person to do all the conversational work, which is really illogical if you think about it. No one wants to talk with a brick wall, since it doesn't do anything back. Do you?
People are inclined to talk about themselves, in general. But they won't usually talk unless another person shows some initiative, some interest in a real back-and-forth exchange. Then, they will tell you just about anything if you are sincere enough, especially since most people they interact with probably don't give a rat's ass about them. I think most of us pass each other like ships in the night... when one person slows down and actually wants to know how you are doing, REALLY doing, and what about that so-and-so event you went to, and how did you feel about that, etc... it really bowls them over, and they open up.
Now, of course, you can also err on the side of being TOO nosy (usually my problem
), but for shy people... that doesn't normally happen. It's just a matter of learning that what you have to say is important, feeling that confidence in your own words and questions... and your desire to really engage in conversation (even if you feel awkward at it) will come through to the other person.
I can't stand overly chatty people, but I *love* a good, intelligent, sincere conversationalist.
I hate to say it, too, but I think a LOT of it has to do with gender. I've very rarely met a woman who can't keep up her side of a conversation in a balanced manner, but I've met LOTS of guys like that. So I've come to accept that guys have gotten the short end of the stick, in most cultures, in terms of being raised and encouraged to express themselves effectively. It's unfortunate, really.