The rules for gaining muscle are simple, but they take discipline to apply:
To gain muscle, you need to eat more calorie every day.
Have your body fat tested to determine your lean body weight and have a personal trainer or nutritionist recommend how much protein you need to gain muscle mass.
Nutritional supplements and meal replacement powders and bars can help increase your protein intake, but they are usually not as nutritious as real food and should not replace regular meals.
Eat adequate amounts of fat (15-percent) and carbohydrates (55-percent). Protein should make up 30-percent of your diet.
Weight train intensely three or four times a week, no longer than one hour per session. Limit your cardio workouts for maximum muscle gains.