To keep things neat and straightforward to the point, never trust internet test or any Socionics tests in general or some random suspicious internet articles, use them as starters and then study the theory on your own to conclude your real type and others' types!!!
It is essential to fully understand the necessary basics of the theory before moving onto typing people. Without a good understanding of the concepts well, one may use stereotypes and false information to inaccurately describe another individual.
When it comes to typing yourself, it is actually harder to type yourself than others because due to various bias that can disrupt your processing which can ultimately disturb your subjective perspective of your objective self. Do not idealize yourself or apply stereotypes of any sort, for instance you don't have to be a billionaire to be a Te base, an enjoyer of sleep to be a Si base, a party person to be a Fe base or a forceful individual to be Se base. Reflect on past experiences, try to focus on the good and bad, including how you presently think of the ways you process information to create a final typing result of self. Another better methods is to ask for other people's opinions to truly receive real feedback, and of course they have to be factual and not biased too. It is harder than most people think to type one's self due to the bias and false evaluations. At the end, I would argue that everyone should see how each IME works in different positions for the functions and blocks and how that fits them due to the ways that the elements work. Of course, one has to fully understand their usage and their different effects and that is when one can easily receive their type. You get to see all kinds of mistyped INFPs and INFJs in the shitty MBTI community, and fuck yeah, they are all mistyped and they idealized themselves and thought of themselves as some sort of saint crap then absolutely fucked up their evaluation of their real character. Don't be like them.
When it comes to typing others around you, it is arguably easier since the truth is that most people wouldn't focus on others for too long vs focus on themselves and their type. It is important to know that person well, and you have to have met them for a long period of time or at least a decent amount of time to the point that you start to notice part of their true nature. Knowing themselves well should be knowing many things about them from their behaviour, worldview to hobbies, a versatile outlook of their chracters that is. Anyone can fake themselves easily in front of others, especially in a business relationship or a romantic relationship, when people try their best to hide their flaws and weaknesses in order to leave good impressions. It is important to see through the masks and the lies in order to type and notice other people's types, as typing their fake selves is completely useless at the end of the day(You get to know that they are fake though, which is a good thing I guess). If you are dating someone new, it is essential to unravel their "perfect image" that is being present in front of you ASAP, since couples always hide their true selves at first and only show it after a few months. When it comes to your family however, it is way better because anyone that loves you will not hide anything(Hopefully) and they will be more honest and realistic in front of you. Typing family members is the ideal place to begin the practice, as you know them very well already and shouldn't be struggling much. Of course, also observe what they are like in front of other people, since they can act warmer and kinder in front of their own cared ones. When it comes to a stranger, it is usually not ideal to type them aside from some basic character traits unless you guys want to further develop your relationship with each other, since a few minutes is surely not enough to know much about someone. Observe what kind of functions they use in real life and in this case the pairing, so in other words not just the base but the ego block in its entire mode. See how they interact with others, if they are very attentive to other people's emotional response and are good at creating a joyful emotional atmosphere within minutes or even seconds, that is a good indication they might have higher Fe to the 3D or 4D extent. Other examples could be if someone is very into the present and always willing to try new experiences while being able to easily take charge and lead the group, they could be a high Se user. At the end of the day, everyone is different but the key to actually typing them is not to hand them out tests randomly despite them being good starting points. The real method and probably the only good method is to get to know them, see them through their masks and discover their true characters.
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In conclusion, some people in real life are easier to type due to being more simple minded and shallow while some other people might act charismatic and helpful on the outside but be totally corrupted on the insider. The difficult of typing others shouldn't vary much but there is a difference in reality. It is mandatory to master at least the basics of the theory and actually get to knowing the other individual in order to conclude their type.