Sounds like you lack a social life altogether. I suggest trying to build a circle of friends first, and then try to game some girls. Social anxiety is a difficult thing to get over, but it's like any other fear...you can desensitize yourself with gradual exposure to it.
Phobias have an extremely well established and successful SPAM method via Cognitive-Behavioral Therapy. Basically, the phobic person is taught to recognize the cycle of fear and how his phobia comes about. This is then followed by a systematic desenstization to the stimulus.
http://en.wikipedia.org/wiki/Systematic_desensitization
Basically you will gradually increase your exposure to social situations, stopping at the point where it is uncomfortable, but not unbearable (remember there is a big difference)--followed by relaxation exercises to associate the stimulus with relaxation.
Once you have become more comfortable, set about building yourself a supportive and positive social circle. This is important because it will provide the people you can rely on and do things with. You can learn a lot from group interactions from your social circle as well.
Lastly, look at every social gathering you get into as a mini-field experiment. Try and recognize patterns in behaviors and test your theories--practice at least one thing every time you go out. Maybe you will learn about body language...start being aware of what other people's body language is. Gradually you will become aware of these little social cues consciously, and eventually they will become unconscious habits (scanning for body language, controlling the frame, etc.).
One site I recommend is
http://www.succeedsocially.com. All free, and has some great tips on how to break out of your shell. I also recommend
Goodbye to Shy by Leil Lowndes. It is absolute basics, but if you are really having trouble, it should help.