In the real world 7% of communication is "the words" and the rest is body language and voice intonation.
In that sense, communicating in the real world is largely about how you're feeling rather than how you're thinking. People seem to communicate emotions to each other, and what happens with people like you and I is we place a very high amount of emphasis on the words themselves rather than the emotions.
There is this feeling of being "inside your own head" which pretty much classifies introverts. I think the real trick to becoming an extrovert is getting "outside of your head".
Some people call this getting "into state".
What happens when you get into state is you stop analysing yourself and stop worrying about yourself, and just express your thoughts and feelings and impulses naturally. Typical people seem to spend most of their time in this extroverted state. Everyone gets "inside their own head" sometimes, but introverts like me seem to do it practically ALL of the time.
If you can recognize the difference between when you are "inside your head" and "outside your head" that can be a starting point for learning how to stay "outside your head".
What I do is I imagine myself projecting my consciousness out into the world. All self-talk ends and I express myself freely. It can actually be a very scary thing to be this way, because when I'm in this state I'm totally comfortable talking to anyone and showing them my true self. For almost my entire life i've hidden my true self, and so this is both exhilerating and frightening at the same time.
When I have conversations with people I try to project myself like that and over time it has become easier and easier to hold comfortable and constructive conversations.
There are many logic-based tips people can give you to make yourself more competant in social situations.
For instance I could tell you to widen your stance - always keep your feet slightly more than shoulder width apart. This naturally projects confidence, and it looks like confidence to other people. Myself, and a lot of nerdy types i've known, tend to stand with their feet very close together, even touching sometimes. This actually makes it hard for others to speak to you because they pick up on your nervousness. People would see that I was nervous by how I was standing, and avoid talking to me because they didn't want to make me more awkward and didn't want to pick up on my awkwardness themselves.
Another big thing is eye contact. Don't be afraid of it. Eye contact is not staring. Keep a normal, relaxed face, and just move your eyes into someone elses wonder what they are like. This might feel uncomfortable (it did to me) but it's actually a totally normal way to communicate.
Another big one is shoulders. Keep them back, and straighten your back.
All of these little physiological tricks can help you to feel more comfortable in social settings.
In my opinion however, the key is that mental switch of being inside-your-head or outside-your-head. Try to observe yourself and see if you can notice when you're in and when you're out. It worked for me, anyway. I can honestly say I have very few issues with nervousness or insecurity in social settings today. I'm not perfect, but I've definitely improved by huge strides. If I had to guess I would say that I started off in a place far worse than anyone here. Which makes it kind of ironic that I was picked to moderate this forum :P
P.S. I think the best way to use this forum is to get thoughts and ideas from people who have experienced similar things, and then try them out in your day to day life.