Idea generation: Two relatively broad ideas are thrust together in my SF. One must be science or tech oriented. In my estimation this is where "unique" counts most, so I try to choose unlikely combinations. Besides unlikely combos, I want the combination of these two ideas to automatically generate conflict.
Character generation: The main character who has to deal with the central ideas must be emotionally invested in them. It must be a person who can't walk away from any difficulty arising from the ideas. The main character must also be a person who is handicapped in some way: physically, intellectually, emotionally and/or psychologically. Handicaps connect the character to the reader, so strong emotional handicaps like fear and desire must be present.
Supporting characters are a funnel for the main character, pressing the main character forward through ever narrowing possibilities in the story. Primary, secondary and tertiary characters need to be necessary to the story. Short stories require fewer supporting characters; a rule I violate too often.
Goal: The MC needs a difficult goal to achieve within the framework of the two ideas, or despite the difficulties that the two ideas create. Goal is so important that I will often think of a great goal and then ideas and characters. No story ends without a goal. I used to pants my stories and they would just keep going, so now I develop the goal first.
Plotting: Inception, introduce MC and direction of story (goal or reason for continuing), ends with the inciting incident (might also be first conflict). First conflict is the point of no return, the MC commits to a goal. Second conflict is the big beat-down and leads to the darkest moments in the story. Third conflict is the climax of the story, the ultimate crisis. Resolution leads to the end of the story and may be very brief. I always plot major events and who is involved in them, but most often go no further. On the other end of the spectrum, I will outline the entire story in great detail, once my outline had more words than the finished story (This happens when I just don't want to write, but need to.).
Milieu: This is world building, background, personal foibles, setting, quirks, costuming, props, language, plot devices. This is the stuff that makes characters and settings real to the reader. An antagonist might be a bully, but what makes her a bully? Is it a desire to make everyone better than herself or a desire to feel superior to everyone? Did she fail in her past? Was her failure significant to the story? Does she wear significant clothes? Does she carry significant objects? Is there something on her office wall that is significant to the story? Know all of the primary and secondary characters as people with their own thoughts and desires. I do character studies.
How does the setting interact with the central ideas of the story? I want to connect my reader to setting, so I make sure to include smells and iconic visuals.
Milieu is a significant pass after the initial write. I make sure that the character dialog is consistent throughout. The reader needs to be grounded in setting with each changing scene. Some call this fleshing out the story, but I try to do as much fleshing out as I can in the initial write. In the milieu pass, I look more for continuity and story immersion.
Correction pass: Final pass before submission. I work backward by sentence. It helps me find grammatical errors and homophones.
That's the tip of the iceberg. This stuff is simple.