A lot of speculative fiction takes place in a futuristic setting. This brings up the issue of needing to create futuristic societies. There is no pre-existing future to base it on. Unlike historical fiction where you can take what is known of Earth history and reshape it to your narrative, you’re on your own to decide what the future looks like.
Here are the key questions to ask:
Is this OUR future?
It’s a fair question. Is this setting going to have Earth-as-we-know-it as its history? If so, you’re working on an extrapolation of the present day into a time period some distance into the future. If you are projecting 10 or 20 years ahead, the world may still look pretty familiar. The farther ahead you push the timeline, the less recognizable Earth will become. This is a balancing act of increased effort in worldbuilding versus putting an expiration date on your work (though you can win bonus points if your near-future-world predictions come true … just look at Orwell).
On the other hand, futuristic doesn’t have to mean our future. Star Wars is a prime example of a futuristic world (even though it was “long ago,” it’s more futuristic than the present day). You get the same ability to present a world, without the baggage of all of Earth’s history. Historical figures can be added to your liking; past societies and religions are fluid (until you publish something); you can mix and match technologies and even leave out things you don’t want to ever have existed (FTL travel, but no nuclear bombs? Advanced materials knowledge, but never cracked the human genome?). A blank slate is both a fresh start and a duty to bring a reader up to speed.
What happens between then and now?
Post-apocalyptic fiction is pretty popular. It shakes things up and is a convenient excuse for forming a new society (or lack of society, in many cases). An apocalypse can leave the world’s history intact, but break the continuity of society. Think of it as a reset button, or the mechanical sweeping arm at the end of a bowling alley. The nature of the apocalypse may be the key ingredient in the tone of the new society that arises, or it may just be a cheap gimmick to start fresh and ignore all those pesky questions (e.g. “why doesn’t the air force just bomb the zombies?”) that would jar a reader from believing in your world.
Another course is an evolutionary approach. Take modern times and give your prediction of how events will carry humanity forward X number of years into your story’s present day. This places you in a hybrid role of futurist, social scientist, and author. You need to extrapolate the technologies that will arise, how they will change humanity, and what society will rise from that. Then you have to convey the feel of that new world to a reader. You can have a brilliant take on how humanity will evolve, but if your plot is a simple murder mystery or love triangle, all that worldbuilding can get lost.
Does history repeat itself?
This is both a crutch and the pearl at the center of a parable. How could past events play out again in a future setting? What lessons have we as humans forgotten, that will come back to haunt us? The fall of the Roman Empire, the Crusades, the Spanish Inquisition, the rise of Nazi Germany, or the Cold War … all can play out anew in a future world if humanity ignores the lessons of the past. Your story can take any of these historical events and rewrite them in that future setting, or such societal misfortunes can form the backdrop of your world as other events take place within it.
In my new Black Ocean series, humanity is putting into practice the old doctrine of Manifest Destiny, except that this time it is expansion across the galaxy. While this doesn’t play a major role in the plot of the first novel (or any that I have planned), its effects are seen in the wider world. Humanity is expansionist, militarized, and convinced of the inevitability of their spread to all corners of the universe. You can see it in the interaction of Earth’s government with its neighbors and allies, in its dealings with rivals, and in the way other species are treated on a personal level.
Are you examining a social issue?
Is our world going to hell? If you can see it coming, or can predict a pitfall we are about to fall victim to, futuristic settings can provide a platform for your warning. This is a classic method for taking a societal ill (real or imagined), or an emerging technology, and creating a world in which it has run amok. This is the premise of many classic novels, including 1984, Brave New World, Do Androids Dream of Electric Sheep?, and even Frankenstein.
In broad terms, the entire Star Trek franchise was built around this premise, exploring various social issues through a rather Utopian futuristic outlook. Often, in the Star Trek universe, it is humanity who is the enlightened species, encountering alien races who still exhibit many of the primitive, barbaric traits that humanity left behind long ago (often in the current age of the episode). It’s easy to go overboard or heavy-handed on this one (Yangs and Comms episode, I’m looking at you), but the formula works.
How does futuristic science influence your setting?
One of the most obvious influences on a futuristic society will be the technology they possess. It’s one of the ways we can eve tell we’re supposed to be in the future. If technology stagnates or even regresses, it’s not really futuristic anymore, even if it the setting is in the future.
So how does technology shape your world? Do improvements in medicine make people less inclined to take care of their health and diet? Does FTL travel make exotic alien food everyday fare at the local fast food place? Does government surveillance oppress the public … or make them feel safe from crime? How would society be different if cancer and most other diseases were cured, and if natural aging could be halted?
You can even take newer technologies from today and posit what life will be like when they become mainstream. Our news is becoming decentralized (who controls what we know?). Alternatives to fossil fuels are catching on (will they saturate the market in time?). Stem cell research is starting to pay dividends (what are its limits?).
There is no end to the questions you can ask. Just remember to always ask them in the context of your story. As always, superfluous worldbuilding is fine, as long as you don’t cram it into the finished work.