Here's my opinionated two cents.
I'm 27 and an introvert and I think that the biggest change that I've experienced these past few years has been to loosen up my thinking regarding what others think of me. This has helped me to be more relaxed around other people, and that leads to body language changes, which again leads to other people subconsciously behaving more positively around and towards me. Later I've come to understood that I was viewed as a cold and non-caring, whereas in reality I was shit scared and stiff around other people. Also one thing that I've come to recognize after reading some articles and doing self-studying is, that my batteries drain around other people, and I need alone-time to recharge them. Whereas for extroverts the drain-charge cycle works exactly the opposite way.
I'm getting a bit off-track here. Let me comment on some of the writings in the comments:
I'm not sure if it's an "america"-thing, but I don't know many people at all that want to talk about themselves. It's not like I would want to talk about myself, I know myself already. Ofcourse that helps the other person get to know me, but personally I think that the other person is immensely more interesting in regards to whom to talk about. So beware of going all-out on making the other person tell things about themselves, one might come to feel uneasy quite fast.
What sn0wBuM said. You need to _actually_ care about other people to keep in contact with them. I apparently don't, because only ever I contact other people when I want to be with them for one reason or another or need something from them. Hence most of the time I dont keep in contact, and that is just the way I am. Contacting someone just to say "Hi, what's up! Long time no see!" and having a half-assed conversation when neither of the party has anything real to say is, in my opinion, one of the stupidest things to do. Though this part of my behavior might be heavily affected by my nationality, Finnish, because we are silent and (look) grumpy most of the time, nor de we have a concept of "small talk". We mean business or we rarely talk.
And while books are good, academic knownledge of how to socialize doesn't do the trick. Actually doing, does.
Meeting new people? Well. You're among people now, so get to know some odd pervert on the net around the same shady corners you spend your time on and you might actually find more deeper friend-relationships than trying to find people offline, where the variety and amount of choices might not be as vast. I found like-minded people at conventions and via board-games. If you don't feel like you fit (for real, not under self-pity), then don't try to fit, and find another kind of people.
Unless your language is unintelligible, then I don't believe for a second it to be a problem. If you're nice person at heart, it usually shines through. But if you are an obnoxious person, you're obnoxious no matter if you master the language perfectly. As long as you get the point through :)
"Making friends is incredibly difficult for adults."
Bull. Most adults try "to be adult" (not jumping with one leg in the air at center of the street etc. "dummy" things), which makes it more difficult to get to know them, because they try to blend in and not be individuals (but they all want to). So if you can overcome _your_ fear of trying to communicate with people, others rarely stop you. (Though don't start a conversation plain-blank on the streets with a stranger in Finland for the sake of befriending them, they might think you are loose from a mental hospital.)
I dont talk much. I don't (can't) take part in conversations because 99% of the time I have absolutely nothing to say. And besides, "it's better to remain silent and be thought a fool than to speak out and remove all doubt". But when I say something, I usually have something meaningful to say, even though if this kind of behavior leads me to being mostly a purpose-oriented person in the eyes of others. I'm me, and if everyone were alike, things would be pretty boring.
It takes all sorts of men to make the society. And in my opinion it's better to be one of those that thinks about these things than to be like the vast majority of testosterone-driven competitive buffs.