People who are struggling to gain muscle mass might find that the problem lies with their diet. They could spend months training at a gym only to find that most of their shirts still fit loosely on them.
It's easy - you just need to add enough to your diet so that your body gets enough ingredients to create more muscle for you. It can easily make what seems to be pointless effort into a true body-sculpting exercise. This can easily help you break through the plateau that you've been stuck on. Even the best body builders get to certain points at which they have trouble putting on more weight; one useful thing you can do is to switch up your workout to hit new parts of your muscles.
The amount of food you eat can stay the same - however, you should mix up the schedule of your meals. Instead of having the standard three meals a day, you can partition those out into five or six meals, with the three basic meals filled in with one or two little meals in between. This will keep your metabolism up and can make sure that your body always has something to use.
The three big meals here are, naturally, breakfast-lunch and dinner. The smaller meals can consist of a lot of things, which can include good old protein shakes or various vegetables and fruits. The point is to keep your blood sugar up, which can keep you from getting hungry and binging, which will ruin your diet.
Healthy fats, lean proteins and carbohydrates are your friends - these are friends you need to meet when you're having your bigger meals. Finding the right balance of protein, carbs and healthy fats is one of the most important things you can do to keep your diet healthy while still allowing you to add muscle.
Muscles need something to be built from, so instead of eating less, you might actually need to eat more to get them developed. Naturally, you'll need to keep eating properly. You can't just eat whatever you want - your diet is still your own personal god.
Continue to increase your intake until you find yourself growing muscle. Once you're growing muscle, stop increasing. When you stop growing, if you want more - just eat more.
After a while, you'll find yourself with a whole new body. It goes without saying that anyone looking to gain muscle has to stick with it and be determined to reach their goals. You're most likely not going to see results over night (unless you're a genetic freak), but if you stick with it and follow the aforementioned steps, you should see results within a few weeks.