Diet and anabolics. Optimize diet with regards to protein and carbohydrate intake. Have your total and free testosterone levels checked, as well as your serum estradiol. If testosterone is low, and it probably is, treat it aggressively with injectable testoserones, skip the trandermals. Treat high estrogen with Arimidex (anastrozole) 1 mg daily. Legal of not in your state, cannibus will help stimulate your appetite.
More to it. There are several ways. Human growth hormone (serostim for example). This is an injection subcutaneously daily. Testosterone (oral or intramuscular) will also help build muscle. Many of my HIV patients are testosterone deficient. Oxandrolone (a oral steroid) is also very very efficient. If appetite is an issue..Marinol (txc) is an excellent stimulus. Megace (megestrol) (an anti-estrogen) works as well.