I've always been a bit introverted, and started college off as what could most charitably be called "painfully shy." I just had to force myself to interact with other people, as myself. I still am uncomfortable around people I don't know, but over time I've learned what's appropriate acquaintance conversation.
One thing that helped me was to rip off one of those "self-improvement" strategies: I made an effort to get to know people with traits I wanted to posess. DO NOT try to be friends with people just to assimilate their personalities -- that's phony and CREEPY. But I found friends I enjoyed, liked and could admire. And I've learned lots that I'd like to emulate from people who I geniunely admire, by looking around and trying to surround myself by the types of people I'd... well, like to be surrounded by. One particularly extroverted friend of mine (who I've known for years now) was recently talking about a very shry mutual acquaintance and said something very profound (to me):
"You know, he's like you used to be. He didn't know how to just hang out."
And I didn't -- I was so socially inept and task-oriented, I had no real idea how to just hang out and get to know people. Maybe you'll sit around playing card games all night... or who knows what could happen. If nothing else, just hanging out is a great way to build up the shared experience and anecdotes that are important to friendships.
One more thing that really worked against me for a long time: Any castoff comment, or gesture, or action, was immediately pounced upon by my mind, and dissected. I spent a tremendous amount of energy in self-criticism and over-analysis. Learning how to get over that REALLY freed me up to have friends, in no small part because getting over that baggage really made me more pleasant to be around. It was a big deal to learn to take myself less seriously. One of the best ways I found to do that was by learning to be embarassed, or put my foot in my mouth, or whatever, and being able to laugh at myself. That doesn't mean being a slapstick stooge, but if you do say something embarassing or feel like you're on the spot, try to laugh it off.
You sound like you're already doing much better than I did. I was halfway through college before I even started having fun with it.
