Having completed and now releasing my Sci-fi novel Retaliation, I have compiled a list of the top ten most important things that you have to consider when writing in this genre. Some of this will spill over to other genres as well and all of it is fairly common sense, but it doesn't hurt to keep it in mind.
Retaliation
Use your own ideas - This is number one because it is that important, there are so many concepts out there it's hard to know if you are the first person doing it, but it is highly unlikely that any two people will write exactly the same book. To be safe though, don't try to re-tread the work of someone else, use your own concept, then when asked you can say how you came up with the idea and it will be clear that you wrote an original story. More importantly you will have so much more fun bringing your own ideas to life.
Use believable characters - we might be basing our story in fantasy but reader need to connect with characters on a real level. If the character is too good and has no flaws then the audience will not buy in to them, if they are too powerful and can't be defeated then you lose the respect of the reader. Characters can be efficient, strong, powerful, weak, evil, good or annoying but they can't be flawless. Try and give them a back story too, everyone came from somewhere and it can help to show the reader how they arrived at who they are now.
Draw your ships - what I mean is that you have to immerse yourself in the world/universe that you are creating, if you are on a space station, then draw it see what it looks like. If like me you are having lots of space battles, draw them, the ships, the battles, who will get destroyed, who will fire the final shot. It doesn't matter where your story is based, draw it the best you can, then you can write about it like it's actually happened. I am not an artist, my drawings are terrible, but they do help me get into my universe.
Find your own terminology - this was a hint given to me by a good friend, try not to get stuck with the same old phrases, warp speed, faster than light drive, tractor beam. This is your world, give it its own identity.
Throw out the rules - Somewhere someone has drilled into us that certain rules apply in these fantasy worlds, vampires cannot come out in daylight, ships can't fire weapons at warp speed, Jedi need midi-chlorians to use the force. I will say it again, this is your universe, your fantasy, what you say goes, even if it is against the tide of popular fiction or science, just do what you need for your story.
Write for you - sometimes there can be a fight between what you want to have happen and what you think a reader might want to see. It is your story, if you want the lead character to die at the end of the book then do it. If you want to switch main characters mid-way through the story then why not, you have to write the story you want to otherwise you may regret never letting the audience see the picture you had when you started writing.
Continuity - 'Danger Will Robinson, Danger!' we are all sci-fi geeks and as such we have an uncanny ability to spot mistakes, a date, a time, an amount of decks on the ship (see Star Trek First Contact) or a character name (I accidently changed my female leads name half-way through the book and almost didn't realise). If you set off on your mission 18 months ago then make sure when you timeline anything you keep that in mind, check and re-check technical data because it will come back to bite you if you get it wrong.
Realism - not just characters, but your universe has to make sense, in Star Wars we see a 60ish year timeline where the ships change, become more advanced but not massively, a good mix of relics and modern which works with the period of time. Andromeda had the one of the most advanced ships in the galaxy become frozen in a black hole then get pulled free 303 years later and it was still the most advanced ship in the galaxy. There had been enough time passed for any dominant species to have evolved their own technology past that point. Keep it real, fantasy is good, but we still have to buy in to it.
The only limit is your imagination - I once read that the show-runners for Dr Who were running out of ideas for storylines, we are talking a about a man who can travel to anywhere in the universe at any point in time that he wants to, how can you be short of ideas? This is your universe, go where you want, do what you want, as long as it makes sense there is no limit to what you can do. Don't be penned in by a lack of imagination.
Have fun - writing is the best job in the world, because you get to lose yourself in the world that you created for yourself, you get to tell stories, use your imagination and build something that others could only dream of. If you aren't having fun with this then you're doing it wrong.