STEP 1: HAVE AN IDEA
Great sci-fi begins with an idea. Unfortunately, as people will tell you, all the good ideas were taken long ago. But that's only true if you believe ideas are indivisible, like, "A guy goes on a journey and experiences personal change" covers everything from Moby Dick to me visiting the bathroom. In fact, ideas are totally divisible. There's no idea that you can't make new by filtering it through your brain.
The way to tell whether an idea is good is to see if it makes you feel like writing about it. There are no other criteria. I know that sounds trite. But it's true. Many people have great-sounding ideas for books but never write them. That means they are bad. The ideas, not the people. The people are probably bad, too. If an idea can't clear the first hurdle in a marathon, a marathon that has hurdles in it, then it's a bad idea. It is as bad as the idea of having a marathon with hurdles in it.
Note: If your idea involves parallel universes, now proceed to all steps simultaneously.
Note: If your idea involves time travel, follow steps in the order of your choice, taking care not to invalidate any future step (relative to you: past step). If you do accidentally invalidate a step, please cease to exist, at least in this timeline.
STEP 2: HAVE A SITUATION
Some ideas sound like good stories but aren't. In science fiction, it's possible to ram an ill-fitting idea into a story, the same way it's possible to force a cat into a little tuxedo, but it takes the same amount of effort and the result is just as awkward. When an idea feels enticing but won't come out, like a cat under the sofa who's gotten wind that you want to put it in a little tuxedo, it's because you have a concept but not a situation.
Stories are about change. A story that has no change in it, or the threat of change, is a painting. And stories that aren't about people are landscape paintings.
So you need to find the situation inside your idea. That's the part of the concept that impacts specific people and causes change to or around them.
STEP 3: INFLATE EGO
Ego is a critical part of a writer's toolbox. Without ego, you'd succumb to the fear that the eighty-to-one-hundred thousand words you're preparing to dump on the world may not measurably improve it. This will only seem ridiculous if you have a tremendous ego, the kind that can look upon a work-in-progress crammed with of plot holes, opaque character motivations, and spelling errors that have dogged you since third grade, and think: Mmm... not bad.
What works for me is telling myself that all writers' first drafts are bad. I can't tell for sure because other writers don't show me their first drafts—probably because they're so bad. You see? So what I hawk out onto the screen in draft one is pretty good, relatively speaking.
Remember the last time you read a novel that was so awful, just getting to the end was tortuous? Someone managed to write that. They typed out every single word. And they did it as a first draft, when it would have been worse. Thanks to ego.
STEP 4: WRITE NOVEL
There are plenty of ways to do this. But all you need to know is that no technique works for everyone, and what's best for you is whatever gets you regularly putting down words and feeling good about them.
This step takes three months if you are Stephen King, 6-12 months if you are me, and a year or two if you have a real job. Add one to ten years if you have small children.
STEP 4A: DELETE THAT LAST BIT
You are stuck and unmotivated. Delete that last bit. I can't emphasize this enough. Delete it. I know you don't want to. I know, logically, it seems like a good idea. DELETE THAT LAST BIT. It's killing you.
STEP 4B: AVOID RESEARCH
I'm unsure whether not doing something can be a step. But that's not important. What's important is avoiding research. I'm serious. Research is useful in two phases: the idea phase and the rewriting phase. In between, research is a stupid boring voice that says, It doesn't work like that. You know what? I'm writing this story, I'll tell you how it goddamn works. I'll make it plausible in rewrites.
Don't tell anyone this, though, because when they ask, "Did you do a lot of research?" the only acceptable answer is: "Yes, I personally lived the entire experience, creating this transcript of actual events." But research isn't what great writers are great at. In the middle of the first draft, research is a distraction from what's important, which is story-telling.
STEP 4: READ NOVELS
I call this Step 4 also since it occurs in parallel. Keep reading books. Yes, their influences will seep into your writing. But what are you going to do, never read again?
STEP 5: DEFLATE EGO
It's fine to leave dangling threads and unrealized characters in a first draft, because you're creating something from nothing. Literally anything you add is better than what you had. Plus, since you're full of ego (Step 3), everything you wrote is pretty damn good, you feel. This is only way to finish a first draft.
But now it's time to read over your story like you just happened across it in your printer's out-tray. Read it like you're a little impatient. Scrawl on it in pen. React to it like a reader.
Then rewrite. I won't tell you how long this step lasts, or how many times it repeats, because it's different for everyone, and the answer is always terrifying.
STEP 6: PUBLISH
This means writing thirty query letters to literary agents and responding to the one who replies asking to see some chapters. The other option is self-publishing, which is also viable if you have plenty of time and enthusiasm for self-promotion.
Either way, though, the best marketing is write a good book. Do that and other people will promote it for you. That's much easier than persuading anyone to pick up a book no-one much likes.
STEP 7: BASK IN ADULATION
Now the good part, where you let the praise roll in. Unfortunately, science fiction people are the most demanding readers in the world. They sniff out implausibilities no reasonable person should care about. They take weak plots as a personal insult. They compare any idea to one better executed in an all-time classic. And they are super visible about it, because they live online.
On the flipside, though, when they like you, they adore you with the passion of a thousand burning suns. So there's that.
There is a reason for this, though. Science fiction readers truly believe in books. They know in their hearts that the world is improved by good ones and diminished by bad ones. They don't read books like consumables. They read them like ideas. And you, as both a reader and writer of science fiction, believe that, too: that this matters. When you think like that, it's immensely satisfying to write a novel. It feels like the best thing you ever did.
Best of luck. You need that, too.