To keep things plausible, you may want to take a couple of months and peruse the TV Tropes list of "So You Want To Write A..." links and examine the ones relevant to your science fiction novel/game. Such as:
- So You Want To Write a Science-Fiction Story
- So You Want To Write a Hard Science-Fiction Story with Space Travel
- So You Want To Create Believable Aliens
- So You Want To Design an Alien Mind
- So You Want To Write an Alien Invasion Story
For science fiction authors and game designers who need a quick plausible scientific non-obvious background to inspire their next novel, there are one or two in this website. Here is a list of links that will send you directly to them.
In his article Staying on the Cutting Edge of Science Fiction, James Wallace Harris notes if you study the history of science fiction ideas, they break down into a limited number of areas:
- Interplanetary travel
- Interstellar travel
- Alien life forms
- Artificial beings (robots, AI, digital life, artificial life)
- Predicting future social structures
- Predicting future politics
- Impact of new technology and inventions
- Impact of new science (anti-gravity, multiverse, higher dimensions)
- Post-apocalypse and collapse
- Post-humanism (mutants, clones, mental powers)
- End of humanity, end of the world
The focus of this website is on interplanetary and interstellar travel. But I have a few odd pages devoted to some of the other ideas.
Here is a mind map of one possible way to divide up science fiction ideas:
- Created Beings
- Interplanetary travel
- Interstellar travel
- Galactic Empires
- Wormholes (reduce the distance to the starship's destination by exploiting an external space warp, natural or artificial)
- Space warp (reduce the distance to the starship's destination by ship's engines warping space)
- Matter transmission
- Hyperspace (make starship's velocity faster than light)
For a science fiction author, nothing makes your stories not age well quite as badly as an over-looked assumption. Sadly, they are almost impossible for an author to spot. And in any event the author has better things to do, like writing the story.
The classic example is all those pulp scifi stories where the protagonists unthinkingly light up their cigars and cigarettes inside their spaceships. If they all perish of asphyxiation by fouling their air supply with tobacco smoke, they will get zero sympathy from RocketCat. But for the scifi authors, everybody smoking like chimneys was just one of those over-looked assumptions. An assumption so universal as to be invisible to the author.
Don't be smug, chances are that your stories will contain similar egregious flaws only visible fifty years from now. Even now young children are puzzled by stories where the protagonists use something called telephone directory yellow pages to find numbers that can be dialed into wall mounted phone. And more recent stories have mysterious things called "dial-up" internet connections, which are cut off if somebody else in the house picks up the telephone handset.
More forgivable is when the author makes a good faith effort to predict the future, but badly misses the mark. At least they tried.
The general precaution an author can take is making a diversion. You throw in some very odd futuristic detail to remind the reader that they ain't in Kansas any more. And hopefully distract the reader so much that they fail to notice any over-looked assumption you mistakenly left in. For instance, Robert Heinlein was fond of mentioning in passing how the door dilated open.
A common failing of with those who write future histories is a failure to take into account Future Shock, that is, the rapid progress of technological advancement. Refer to the "Apes or Angels" argument. Consider that one hundred years ago the paper clip had just been invented, Marconi had invented the wireless radio, the Wright brothers had invented the airplane, and the latest cutting edge material was Bakelite. Assuming that technology continues to advance at the same rate, all of our flashy technological marvels of today will look just as quaint and obsolete in the year 2100. And in 2500, they will look like something made by Galileo.
Remember, this assumes that the rate of technological progress remains the same. The evidence suggests that the rate is increasing.
When it comes to futures histories in various SF novels, the main failing I have noted is a failure of scope. While you may read novels with orbital beanstalks, immortality drugs, virtual people living in digital cyber-reality, nanotechnology, transhumanity and post-humans, Dyson spheres, teleportation, zero-point energy, matter duplicators, time travel, cloning, and cyborgs; you almost never find an individual novel that has all of these things (although Greg Egan's DIASPORA comes close, and the Orion's Arm project comes even closer).
This is because future history SF novels are not meant to predict the future, so much as they are meant to illuminate a specific point the author is trying to make.
This topic is gone into in more detail here.