I have found that over the years just going to the gym, starting with a basic work out, and learning what to do or not to do from the regulars has been a good technique. It is a good way to learn, and although I wouldn't say I go to the gym to socialize, I have made some good friends along the way. The muscle mass won't happen over night, but it will come as you continue to move heavy things around.
"Most men stop when they begin to tire. Good men go until they think they will collapse. But the VERY BEST men know that the mind tires before the body and push themselves beyond all limits. Only when all of these limits have been shattered can the unattainable be reached." ~Dan Gable