Top 4 Pro Tips To Natural Gain Muscle

TIP1: MAKE A EATING HABIT
To gain weight, you need to focus on making your meals a habit rather than an afterthought. Your body is pre-programmed with your genetic disposition. And in your case, you have a very fast metabolism that digests and burns calories quickly. So even though you might eat 3 meals a day, and they may be high calorie meals, your body is going to burn through these very quickly. Instead focus on having 5-6 meals a day spaced 2-3 hours apart so that your body is constantly being provided with something to metabolize and build muscle.

TIP 2: STOP RELYING ON SUPPLEMENTS
I have been in your shoes, and I can't count how many times I have fallen prey to the supplement industry. You have to understand, a supplement is exactly as the name implies...A SUPPLEMENT. It is not going to make or break your gains in the gym. The majority of supplements being marketed to hardgainers looking to gain weight are focused on increasing water weight instead of muscle which after you come off the supplement, your weight will drop again. 
TIP 3: TAKE IT EASY
As naturally skinny guys, you have to stop moving around so much. It's just a part of who you are, but you might fidget or move around a lot in the day. Learn to relax a bit more and try to limit activity outside of the gym as much as possible when outside of the gym so that your energy is put forth to good use.
TIP 4: UNDERSTAND CALORIC SURPLUS
This is another thing I am very tired of hearing. 'No matter what I do or what I eat, I can't gain weight'. I have heard this countless times and I am here to tell you that you are dead wrong. That's OK, because I actually said the same thing until I realized the truth. Most people think they are eating a lot and you just may be. But no matter what you are eating, if you are not gaining, you are not eating enough. Most times, you should re-evaluate your diet as well and focus on more calorie dense foods. But you need to eat more if you are not gaining.