How do you come up with poses??
I’m not exactly sure which answer you are looking for, but I hope that you will find it in this dreadfully lengthy response.
In my opinion, drawing a pose requires the understanding of two different but related things: human form and body language. Either can be achieved by observing people, each in a different way.
The first is by learning the many aspects of anatomy, which is an endless path of repeated exercises. For body language, you have to look at how people hold themselves when they behave in a certain way. Live drawing is great, as it teaches you both at the same time.
Just watching people be, doing stuff, interacting with each other, has provided for great material that I can apply to my own characters, especially regarding their personality.
However, their personality isn’t necessarily why I portray them in a certain way. Instead, it’s based on how I want other people to see them as (for example, drawing an antagonist, but not explicitly showing they are one).
Taking into consideration who the character is and what I’d like to express about them, the formula for the pose itself would be something like:
Angle + form of the body + gesture + facial expression = final pose.
I could give you so many examples for every part of this quickly invented formula, however for the sake of this response, I’ve doodled one example in which I’ve combined all these elements, and elaborate on associating a pose with body language. Please note that this is my personal interpretation!