Once you have the mentality you'll have to change your lifestyle.
Sleep: You'll need to sleep properly (go to bed early and wake up early but sleep a lot) because sleep is what make your body and your muscles grow.
Diet: After that you'll have to change your diet, from fat to protein and carbohydrates food. It works like this: Protein use carbohydrates to make your muscles grow. It's like, carbohydrates are the raw and proteins are the workers that convert the carbohydrates to muscle.
Supplements: Consider using a supplement (optional).
Water: Water is an essential ingredient for muscle growth.
Workout: Workout is the most important point in getting muscles, but just all this points together, in a perfect balance, will make you get the body you want.