Do weight training at least 3 times a week
When you train with weights, your muscles will grow. Also, it is important that you gradually keep increasing the weight with which you train. As you train, your strength will increase and you shouldn’t find it exceptionally difficult to do so. For instance, if you are doing lateral pulldowns with 30 kilos of weight, try and increase it to 35 kilos the next time.
Consume 300-500 calories more than usual
Eating 300-500 calories more than your normal intake may not be easy, but you must do it if you want to stop being skinny. Make sure you don’t do it just by overeating at once, but instead do it gradually over the whole day. You may also want to have a look at these foods and their calorie count so as to fulfill your daily requirement.