The first tip is to plan. If you don't plan exactly how to gain weight or how much to eat, you are going to have a bad time. This is because our body will deplete muscle and fat together in the aid to limit the amount of calories we burn. That is done by decreasing muscles which will reduce the amount of calories you use and by using some of the fat you have no matter how little it is. This results in a situation where your body is highly susceptible to storing fat rather than building muscles, leading to undesired results. The basis is to consume 3500 calories as a gauge and increase the diet by 500 calories until you start seeing either your belly growing a bit or your muscles start to develop. It will take roughly a week in order to gain 1 pound of muscles so there is really no need to rush to put on more weight than that. In a month, you should look to put on 4 pounds or around 2 kilograms of weight.
Like I mentioned, calories are important in an ectomorph diet. If you do not consume enough you will not grow, despite all the supplements or protein you may consume religiously. Your body will only absorb so much protein so there is no point feeding more than what your body needs. Your diet should be made out of around 50% carbohydrates and 30% protein.
Since we are on the topic of diet, let me share the importance of being consistent with what you eat and tracking it. The simplest way to track is to eat the same thing for a month and see if it produces results. If it does, stick to it. If it does not, eat more. This is because people tend to choose what they want to eat differently each day due to the sheer amount of choices we have, and also to tempt our taste buds. However, this does not work in the favour of an ectomorph unless you can track in complete detail what exactly you eat and consume only whole food which is prepared by you. Since this can be hard to achieve, I recommend you to stay consistent with what you eat and change things up if they are not working after a month.
Marking progress is important if you want to know if your diet and exercise work. The idea is to weight yourself once a week so you know how much to improve, rather than be burdened by the fact that you are far away from your results.
Speaking about pressure, remember everything you do is to let you move closer to progress and not further away. I have seen people give up even before they gain it simply because they find it too difficult to do. Just because something is difficult to achieve does not warrant giving it up, but rather just separates those who want it badly enough from those who are simply giving lip service. Hold on and allow time to work its magic on you.
Having a friend around with you in the gym ensures that you will train properly if you are both hardworking. Find one person who you can help and who can also help you. This habit of doing things ensures that you will pick each other up at the lowest point in time and push each other forward when the going does get tough. That is the reason why so many people are hiring fitness trainers to help them gain or lose weight.
A key crucial thing is to simply make your actions into habits. Push yourself in the beginning so that when you are tempted to throw in the towel literally, it will make it uncomfortable for you to stop. If you have a solid timing when to eat, when to sleep and when to train, it will solidify your goals more firmly in place.