In his excellent book on self-experimentation, The 4-Hour Body, Mr. Ferriss describes his process of putting on 34 lbs of muscle in 4 weeks.
A brief discussion can be found on his blog in the Geek to Freak post. Even if you don't read the entire book, you should at least pay extremely close attention to the "six basic principles" on his blog post. You will add size just by following them.
Mr. Ferriss follows a minimalist approach to training. Using only a few exercises and a minimum low volume all out set routine.
1. Pushing movements
2. Pulling movements
Stay strong my friends!