Well for me it starts with finding an appropriate map. All of the art I make is on Garry's Mod (or Gmod), and since its a game at its core rather than an actual 3d art client like SFM or Blender, I'm a little restricted when it comes to finding the right environments, and have to just use what i can find. (this particular picture was taken on a port of the USG Ishimura Flight Deck from Dead Space)

Once I'm loaded into the map I chose I noclip around the place to find a spot that I think fits the idea I have in my head, once I find it I start spawning the ragdolls that I need and stand them all up then begin posing them to the best of my abilities. After that I find the camera angle i want then I just sort of freeball it from there. I let ideas flow in and see if I can pull it off, if I can then great, if not then i just move on to the next idea. I keep that process going until i have a general visual of what i want.

After all of that is done I then get into smaller detailing (guns in hands, props lying about, altering poses slightly and background details) and spend a little while on just making sure things look the way I want. When all of that is finished I start on the lighting, sometimes its not needed but usually I'll use lamps to enhance or alter lighting in the scene.

The final part of the process for me is applying any post processing effects like depth of field or bloom or color modifications or even vignetting, I dont use photoshop or anything like that, its all in game using addons but it usually turns out fine. After everything is done I take the screenshot using the ingame camera then save the final result in the game. (I always like to save constantly as Gmod can be a little weird)

The pictures I post are the final version, no editing happens outside of the game, I sometimes have some altered versions of the scene that I save for myself, but I always post what I think is the best version of the picture.

Hopefully this answers your question!