1. Increase calories gradually
In order to gain muscle mass you should eat more calories than you burn. Eating more is, however, is a very broad term. once you establish an approximate maintainance calories intake uptake, add an additional 300 calories, no more. Gradully you will start gaining weight without getting fat. After a period of several weeks add an additional 300 calories. Continue like this until the end of your bulking phase, but don't add more than 1500 calories for the whole period. The slow introduction to new calories to your system will make it adapt and rise your resting metabolic rate, .hich increases your capacity for food consumption and muscle gain, without much fat deposition.
2. Quality over quantity
When bulking you should be concerned not only on how much food you eat, but also on WHAT foods you eat. The quality of the food is very indicative of whether it will be digested and used by the body efficiently, or it is more likely to be stored as fat. Thus, I recommend you choose foods sources that provide quality calories. For example: you can get 100 grams of carbs from 1liter of coca cola, but you can also get them from 150 grams of brown rice. In this situation the sugar-filled beverage will create huge insulin spike, which will make you retain some of the extra carbs as fat, while the complex carbs from the rice will provide you will long lasting energy and fill the muscle glycogen stores much more efficiently.
3. Do not do bulking for too long
Too many people do bulking for too long. We all have those friends who are on constant bulking for the past several years, a.k.a. permanent bulk. Why is this not optimal in the long run? The body is a very complex system, which quickly recognizes and adapts to whatever it is forced upon it. In a typical bulking phase carbohydrates are increased, as they provide the easiest and cheapest source of energy. The maintenance of high levels of carbohydrate consumption for long period of time causes a drop in insulin sensitivity. Lowered insulin sensitivity means that your body doesn't ond to insulin very efficiently and this creates a "damaged" glucose deposition and usage system, which will ultimately lead to more fat deposits and less muscle glycogen.
My advice is to do bulking for 2-3 weeks followed by 1-2 weeks of lowered carbohydrate intake. Another way is to eat high carbs for 2-3 days of the weeks, followed by 1-2 days of low carb consumption. This cycling will help maintain good insulin sensitivity and the body will continue to use carbs efficiently and prevent unwanted gain in fat. Carb cycling is essential for optimized muscle growth and fat loss!
Gainning muscle is not that hard. Practice these and see the diffrent.