Food rich in protein and calories are best for gaining muscle so include milk, eggs, fish and chicken in your diet for natural sources of protein.
Have lots of carbohydrates in a combination of simple and complex carbs. Increase your portion size.
If you are a vegetarian, have pulses and legumes and dairy products like milk, yoghurt, paneer, etc. It is necessary to take
protein supplements with workout because the body requires higher levels of protein which is usually not met by diet.