Wow, been there for sure. I would recommend taking note of those social situations that cause you anxiety. It could be calling someone on the phone, approaching someone to ask a functional question (e.g. what time is it, was there any homework for our class, etc.), asking a school-only acquaintance if they want to go see some band that's in town, whatever. Then just thoughtlessly enter into those situations, and try to build up a mass of experiences pertaining to them. This way, your intuitive idea of what those situations are like won't be determined by nervous speculation and over-thinking, but actual memories that you have. At first it will be just as hard as you expect it to be. This is something that took me way too long to figure out: over time, with repetition, the experience of being in those situations will completely change. They will become more manageable, and eventually you'll start to have times when you feel no anxiety, everything clicks, and you handle the situation masterfully. That's James Bond. But the only way to get there is by plowing through the painful introductory phase. Experience is the best teacher. It's really the only teacher for things like this because it's all about intuition and building an intuitive sense of social wisdom. My mistake when I was your age was wondering too much about "how" I could successfully do certain socially difficult things, like going on a date with a girl and being charming. I spent all this time worry about finding the "way" or "techniques." But before you have experience, there is no way. It's impossible to perform; nobody can help you; nobody can explain it. You simply need to walk the walk and fail over and over. That is the only way to gain the serenity necessary to enter into a situation and keep your wits about you enough to focus on the situation, and not your anxiety about the situation.

tl;dr - Fail as much as possible.