You can follow the below things in order to gain a good amount of muscle:

1. You need to increase your caloric intakes by about 500 to 1000 Calories per day. Extra 500 Calories/day will help you gain up to one pound in one week.
2. Eat your three main meal (breakfast, lunch Dinner) spaced about 5 hours apart. In addition eat two to three snacks a day in between meals.
3. Snacks should be of high calorie such as milk shakes, yogurt, high carbohydrate food- banana.
4. Eat more complex carbohydrates like whole-grain breads, pasta and Brown Rice etc.
5. Never skip your breakfast. Include one eggs and fruit juice to your breakfast.
6. Eat bigger than normal portions for your regular meals.
7. Eat food with higher calories, Moderate fats, Higher Protein, Higher Fiber, Higher nutrition.
8. Choose high-quality protein sources such as eggs, meat, fish, milk, seeds, protein supplements etc.
9. Since most of the calories for weight gain come from carbohydrates and fats, do not replace them with protein.
10. Eat starchy vegetables (Potatoes, Peas, Cauliflower, Pumpkin, Sweet potatoes).
11. Consume nuts, calorie dense ripe fruits like Banana, dried fruits like dates as snack between meals.
12. Eat the right kinds of fats. Avoid Trans-fats. Add healthy unsaturated fats in moderation such as olive and canola oil, nuts, seeds, peanut butter, avocados to your diet.
13. Do not drink water before meals. After meals, wait about 10 minutes before drinking water.
14. Beverages can help you gain a weight too. If it is possible, drink shakes, milk, juice, etc. instead of tea, coffee and diet sodas.
15. Do 30 minutes of resistance training. Weight training helps to convert the extra calories into muscle, hence add some extra pounds to your body.
16. Aim to lift a heavy enough weight that you’re fatiguing within the 8-12 rep range, completing a total of 2-4 sets for each exercise.
17. Do NOT engage in aerobic exercises (Running Stationary Bicycling). Aerobic exercise help you lose body fat (weight loss). You may lose more weight than gain weight.

In a nutshell, you must increase your intake of good calories and encourage the right kind of cellular growth through weight training .

Hope this helps.

Thank You..!