If you want to increase muscle mass and gain weight, remember that in order to effectively bulk up, you will need to be persistent in your efforts. Increasing your caloric intake is an important part of gaining weight and building new muscle tissue. When you feed your body more food than it can burn, you gain weight. Weight training is also an important part of gaining weight and increasing your muscle mass. Weight training stimulates the muscles and promotes growth. The combination of weight training and proper diet is the best, most effective way to gain weight and increase muscle mass continuously over a period of time.
Infographic source: Bones To Beast