Many times science fiction and fantasy merge into each other and it is hard to tell the difference. There is a lot of disagreement about what science fiction is and what fantasy is. Basically, science fiction deals with the future, hardware and technology; fantasy deals with things magical, mythical and medieval.
If your imagination runs wild, writing science fiction and fantasy is full of possibilities. You can go wherever your mind wants to roam and play. You are the one who sets the rules, develops the society, creates the races, determines the paths lives will lead. In other words, you get to play God. Hasn’t everyone had a fantasy to play God, at least for a little while?
You don’t need to be a scientist or have vast scientific knowledge to write a great science fiction story. Scientific theories don’t have to be explained, just described or named. Use your imagination.
No one really knows what the future will be like, what new inventions are around the bend. Governments that are now democratic and free might possibly turn into tyrannical dictatorships. Governments that are now tyrannical dictatorships may turn into freedom loving democracies. World peace could be disrupted by an overwhelming natural disaster that destroys half of mankind.
Space, the final frontier, might be where you want your story to be set. Maybe even in another galaxy. Science fiction could be used to write a spy story, a thriller, a mystery, a western. Whatever your heart desires.
Science fiction has always asked questions that society isn’t quite ready to face yet -questions about nuclear power, race, pollution or environmental damage, for example. You could write about encounters with aliens, time travel, fear of the unknown or altered histories.
Some great science fiction books to read are The War of the Worlds and The Invisible Man by H.G. Wells, The Andromeda Strain and Jurassic Park by Michael Crichton, Journey to the Center of the Earth by Jules Verne.
When I think of fantasy, I think of King Arthur and the knights of the round table. I think about fairies, elves, and unicorns. But I also think of witches, sorcerers, and dark lords. Evil can abound in the world of fantasy.
Fantasy can also ask questions that society isn’t ready to face. Issues like equality of races and the death penalty are just a few of the options for a fantasy story.
However magical your world is, you should write about it so convincingly that your readers believe it is real, that they believe it might actually happen while knowing that it is make-believe. Though you don’t have to say why your world is magic, you need to know the reason why. For every magical thing that happens, there should be an equal and opposite reaction. Any good magic should have a bad effect somewhere. Likewise, any bad magic should have a good effect somewhere. Remember, just as your actions have consequences so should the actions of your characters.
Magic in your world should touch every part of your characters lives. If the magic in your world is advanced enough, counterparts to modern or future technology will be present. They would have their own versions of telephones, cars and computers.
J.R.R. Tolkien is one of the best known fantasy writers. The Hobbit and The Lord of the Rings series are awesome works of fantasy. These superb works have all the major ingredients of fantasy - magic rings, ghostly horsemen, goblins, dark lords, giant spiders, ugly trolls, beautiful princesses, elves, a good sorcerer and an evil sorcerer.
Piers Anthony series “The Magic of Xanth” has made the author a tremendous amount of money. I have read the first 3 or 4 books of the series and really enjoyed them. After that, the fantasy became so far-fetched his world was no longer in the realm of possibility for me. I no longer believed what he was writing. Rules seemed to change out of nowhere and it seemed to me that he wrote stuff off the top of his head without checking to see that the rules of his magical world were followed. Or maybe his magical world had no rules. Anyway, I do recommend reading the first three books of the series - A Spell for Chameleon, The Source of Magic, Castle Roogna.
Some more great examples of fantasy are books by Holly Lisle. Books in the “Secret Texts” trilogy are Diplomacy of Wolves, Vengeance of Dragons, Courage of Falcons.
One of the best ways to learn how to write science fiction and/or fantasy is to read good books in the genre. Read the books I’ve recommended above, take them apart and look at how they were written. Then take one of the storylines and write a story from it with your own cast of characters in a world you created with its own set of rules. The story you write should be completely different and bear little if any resemblance to the one you from which you took the storyline.