Please read the other posts in this series first.
Here we will examine Constantin Stanislavski's “method acting” and a small bit of intel gathering via people watching. He wrote three books on this so the post will be condensed a bit. Strasberg vs Stanislavski both call their system "method" acting but Strasberg's is a "fork" - it was inspired by Stanislavski and is a bit different. The Meisner Technique is the "opposite" of method acting and worth looking at if you get time. There are other acting methods as well.
This approach requires the actor to be incredibly empathetic and even do research on the person/people in question to present a “true/natural” representation of the character to their audience. Stanislavski was big on people watching intently while paying close attention to detail and this is a great method for basic intel gathering.
I'll cover the technique more in the next post but start off focusing on just one person or type of person - focus on mannerisms, accent, body language, facial features, habits, wounds/callouses, dirt/cleanliness, SES/education level, and style items such as clothing/jewelry/accessories etc then try "portraying" yourself that way. A great example of this is Greg Iddon's "bring a ladder" trick from Ip Expo 2016. You may need to take notes at first but want to eventually "ween" yourself off this by only taking mental notes - feel free to google around for memory tricks and mnemonics etc.
Also - start off with someone "closer" to your natural personality and slowly work your way to more "opposite" personality types. Stanislavski would practice these skills by trying to "blend" his character into the crowd with common folk during down time. It's typically best to practice these skills in "everyday" situations before relying on them for something serious; practice by making up SE games/goals just for the hell of it since the risk is low and it gives you room to make mistakes (which is how you learn).
Hang out at an eatery/bar in your local airport and study pilots. Converse with a few, prod them for job experiences (maybe say you are interested in possibly becoming one), get an idea for the dress code, lingo/jargon, how they conduct themselves, and find some forums online to data mine etc. After a while try "acting the role" and interacting with both pilots and non-pilots alike.
Connecting the mental and physical realm was big for Stanislavski and he felt that actors could give depth to their role through this link. Actors should be "in character" as often as possible - on stage, in rehearsal, even when not required by the script to speak or feel a certain way. If the script puts your character into a cold climate without a jacket he would say that you should emulate physical characteristics of being cold by shivering, changing position, warming your hands etc. This helps keep the actor thinking of the character as a "real" person as opposed to just another role they are playing.
The "Magic If"
This is meant to get you into the mentality of your character - questions like "If I were there, what would I be thinking?" and "If I were my character, what would I be thinking?" are two of the biggest questions to focus on. The end goal here is to be deeply empathetic with your character.
The Given Circumstance/Truth and Belief
This accompanies the "magic if" and goes back to our bit on wearing masks via Perspectivism - actors must accept their given circumstance/context as "valid" and relevant to their role even if it conflicts with their personal beliefs. Stanislavski defines this as the play's narrative; its facts, events, epoch, time, setting, conditions of life, interpretation by the actor and director, and the design element such as costumes, lighting, and sound. In the real world this means very similar things such as an irrational fear of dogs, belief in a different religion, callouses on the hands of hard laborers, mud/paint splatter on the boots of a carpenter/electrician, or a city inspector insignia on their hardhat.
Similarly to "The Given Circumstance" Stanislavski mentions "Truth and Belief" in which he says stage truth is unlike real truth. Stage truth is not really true but simply suggested to be true by the actor.
Actors do not have the "full story" of their character and neither will you - try to find hints within the context and information you do have. This includes visualizing these motivations in a similar way to how athletes visualize their swing or winning the game; think about who you are, where you came from, why, what you want, where you are going and what you will do when you get there. Even better - create your own stories to "build your character" in the minds of others.
Circles of Attention
This is meant to help actors remain calm while acting by focusing on something, say a prop or other actor, very intently and creating a "circle" of perception between you and the other item. This is similar to the common advice of focus heavily on other people's reactions in order to hide your own; the main idea here is to take the "spotlight" you usually use to analyze yourself with and turn it onto something externally focused. It's hard to worry when you are busy actively interpreting someone's actions and body language.
Before being able to portray subtle nuances actors must be aware of the other members of the cast and the roles they play in relation to the actor - think back to the story telling post and how we "...need to be aware of not only where you are in the cycle but also where others around you are; this includes parts they play both in their own version AND your version of the story.".
Many times actors will rush lines or draw them out in the wrong spot which can hurt the performance; for example a father who just got news of his son's death my have slower, broken/mumbling speech for a while yet someone who just got their dream job may be crazy excited with their mouth going a mile a minute.
Stanislavski mentions drawing on "emotion memory" to add a level of realism and emotional depth to the character but it's a controversial aspect of acting theory.
He also mentions Units/Objectives and a "Super-objective" but these are more geared toward acting - they can be summed up as keeping in line with the story/role you are portraying and the overall "feel" you are going for both in the long and short term. Keep in mind that there are many subplots involved with the "main story line" that can occasionally reveal a trait or two about the "character" - not many stories, plays, TV shows, or movies only deal with the main "story" so don't rush when trying to tell yours.