I learned my social skills mostly through observation and trial and error. I'd watch other kids in school, see what kinds of body language they used in specific social and emotional contexts, and try to figure out how other people reacted. Ditto for tones of voice and word choice. I also spent a lot of time mentally mapping out social relationships between my peers in as much detail as I could and tracking them over time, but I don't think that part yielded too much in the way of useful skills or information.

Whenever I thought I had some small piece of the puzzle, I'd find a context in which I could try it out, fail horribly, try to figure out what I did wrong, and try again. Once I'd realized that the only common element in all my social failures was me, it took me maybe 2 years to hit a level of basic competence, with gains coming slower after that.

I also benefited from bouncing ideas off of a therapist on a regular basis, though I suspect any sympathetic adult would have been about as helpful; the most useful part was being forced to clarify my thinking in order to coherently explain it to someone else. And having a low-pressure test environment didn't hurt, either.

A couple disclaimers:

• This approach worked for me, and it has worked for some other autistic-spectrum people. (I have Asperger's, FYI.) It may not work as well for you, or at all.
• If it will work for you, this is likely not the best, fastest, or easiest route.
• The brute-force approach is hard and unpleasant. You have to be willing to fail over and over in what are often highly embarrassing ways.
• Rehabilitating your reputation in the social circle(s) you use for practice will be all but impossible.

Hope that helps.