Hi Sunish, i would suggest eating 2 eggs, 2 bananas, a boiled potato and one full glass of buffalo milk daily. You can gradually increase the quantity to 4 eggs, 6 bananas, 2 potatoes and 2 glasses of buffalo milk daily. If you eat nonveg have chicken atleast twice a week. Also a bit of exercise is necessary. Have a 3kms walk daily or join a nearby gym. And yes, equally important is good sleep/rest. Also drink atleast 5 glasses of water daily. There are other diets also. But this is one of the fastest ways you can gain weight. You will see the results within 2/3 weeks. Thats what I did and gained weight from 56kgs to 69kgs.