Yes, I'm yet another one of those multi-book epic extravaganza folks. I've probably written about 100,000 words of prose, edited into more or less finished stages, over the past several years and here's the depressing part:
I had to toss it all and start from scratch.
Yknow why? The premise didn't work! I had a premise that didn't place the main character in the center of the action. Which didn't seem so bad at first...but as the story evolved, I found it harder and harder to finagle the guy in the center of the story. I took a good hard look and realized:
1. A different character needed to be the central character (who I wasn't even that interested in!)
2. My main character needed an entirely different premise for him to deserve main-character-ship.
I opted for #2, since it's chiefly my affection for the characters that keep me motivated to write. And a lot of the character-building, universe building and even parts of finished scenes can be revamped into the new premise, plus that 100,000 taught me how to write, so it's not a total loss. (The usual axiom is that whatever your first novel is, you'll have to toss it out - that's just for practice.)
My main advice then is, start at the start. Don't jump into writing actual finished prose. Think your premise and your characters through and map out where you are going with them. Don't take the risk of running into a brick wall after several years of effort. (Or, take the risk and figure it's a necessary learning experience anyway.)
And thinking about some common amateur mistakes, here are a few I've seen frequently:
1.
Mary-Sue-ism. It ain't just for fanfic. Having characters who are too damn perfect and obviously just the writers' wish-fulfillment is very jarring and makes the writer look like some kind of arrested adolescent. I've seen published novels that make this error, just less blatantly than the fanfic. A good solution is an unreliable narrator (meaning someone who is not a stand-in for the writer's psyche).
2.
Impoverished description. This seems to be a symptom of writers who don't read and would rather be writing a TV or movie script. They limit themselves to sight and sound, but the other senses are conspicuously missing.
3.
Out of control description. You really don't need to describe everything your character is wearing and every object in the room. Choosing a few elements that create a full sense of character and place is a hard trick but well worth cultivating.
4.
Characters who talk too damn much. If you're an accomplished writer, you can try unusual formats such as almost-all-dialogue (or, almost-no dialogue if you prefer). But huge chunks of poorly written diatribe from your characters is generally not a good idea. Especially if you have this guy in your character list...
5.
Captain Exposition. It's very obvious when a character is saying something just to convey information the reader needs to know. Respect your readers' intelligence that they can get by with a certain degree of ambiguity (like leaving out the details of a room, knowing how much you
don't have to say is another one of those nifty tricks) and respect your own talent that you can convey needed information in a more artful form.
6.
Taking too long to get to the beginning of the story. Figure out your story and then lop off the first part because it's boring. I don't even need to know what your story is to know that. All stories have a ramp-up period before the gigantic glob of space goo attacks. Start with the space goo and if you need to fill us in on the backstory, dole it out in flashbacks along the way. But above all, don't take the chance of losing the reader's attention in the first paragraph.
Hmm, none of that relates specifically to science fiction, does it? That just goes to show that there aren't separate rules for good science fiction. Just make sure it's good fiction.
As for tips-find a situation/location/time of day etc where you are both alert and comfortable, let your mind wander over your planned story until ideas come to mind and then write them down. That's really all any writer does.
That's like 2% of it (the fun 2%)! All you end up with is a stream-of-consciousness jumble. The other 98% is hammering it into some useable shape.
I'm a gardener but I have a concrete mixer and a backhoe because if all you have are plants, that ain't no garden.