What are the better ways to increase body weight?

Body Weight: A combination of a sensible diet, prescribed by a nutritionist, and a proper exercise plan, usually results in both a cosmetic and medically healthy weight gain. All things being equal, assuming a normal state of health, you should achieve good results that way in a few months.

Increase Muscle Mass: If you want to improve your body weight and you are normal body composition, increase muscle (lean) mass or fat free mass. Muscle weighs more than fat and this will improve your metabolism as an added benefit. Consult a personal trainer who can direct you with diet, weight lifting and aerobic exercise. This is the "triple" approach to body building.