The small details you include in your narrative make a huge difference to how the reader perceives the setting. It’s one thing to say a character made a phone call. Is her iPhone connected by Bluetooth to her car’s stereo so she can make the call hands free? Is she dialing a rotary phone and waiting forever for the dial to spin back after a 9? Does she lift the earpiece of a candlestick phone and ask the operator to connect her?
These two items on the Elements of Fiction Editing Checklist are related—pick the one that fits your novel:
☐ If the story is set in the past, historical details are accurate.
☐ If the story is set in the future, scientific details are plausible.
Both of these points require doing your research. But don’t let research keep you from writing. Be willing to stick in a note (could you telephone Paris from London in 1890?) and fix it later when you learn that no, the submarine cable between England and France wasn’t laid until 1891.
So write your first draft without worrying too much about specifics, and then examine your manuscript during editing for places where you need to do more research to fill in the details.
Keep your viewpoint character in mind and remember that the things that are important to the character are the things you need to spend the most time on. So if the character is a stock broker who spends a lot of time on the phone, you might spend some time describing his phone and how it works. But if the phone is just there to deliver one plot point, and it’s not of ongoing importance to the character, don’t spend a lot of time on it.
This is the handwavium you’re looking for
In science fiction, there is a certain degree to which modern science can only take us so far, and after that we have to start making things up. But where science can define what we are depicting, we must use it, and know what we are talking about.
It’s all well and good to say we can flit about between star systems because Warp Drive or Hyperspace or whatever—that’s handwavium or, as the folks over at TV Tropes call it, Applied Phlebotinum. You make something up and trust the audience will go along with it.
But if you’re going to accurately describe an interstellar voyage without using handwavium, you have to consider actual scientific matters like what kind of fuel the ship uses and how long it will take to get where it’s going. Will you have a sleeper ship or a generational ship? If you have a generational ship, what are they using for food?
Notice that our checklist item says scientific details must be “plausible.” You don’t have to calculate precisely the power needs of a cryogenic suspension system that can hold a crew in stasis for a hundred years. You just have to make your descriptions realistic enough that the reader’s suspension of disbelief won’t be broken.
UPDATE: Over at the Writing Excuses podcast, guest Brad Voytek coined the term “elegantly incorrect” to describe fiction that describes science that’s almost but not quite yet in existence, citing Isaac Asimov’s science fiction series Foundation and Richard K. Morgan’s cyberpunk Takeshi Kovacs series as examples. Stuff that doesn’t exist yet can’t be described in detail, but we can get close enough.