In sci-fi and fantasy, the world in which your characters, and, indeed, often your narrator(s) exist is vastly different from our own. What we would normally compare things to, these characters/narrators would not. Thought and care must therefore be used when choosing the vehicles for your similes and metaphors.
Now, the simplest way to deal with this, in third-person at least, is to say "well, the imagery is intended to show the reader what things are like, and the reader exists in the real world not my fictional one" and two compare things to everyday objects.
I, personally, find this terribly jarring. You're reading about spaceships doing battle and, suddenly, a comparison is made to our world. The reader, I feel, is kicked out of the story's world and abruptly dumped back into reality.
In first person, this is of course even worse, as the narrator is generally supposed to be an inhabitant of the fictional world. This came to my attention when Chris Miller criticised the lack of imagery in my tale,
Trench 37b. I read over it, and found that, while I did use a number of similes and metaphors, most were fairly broad and often even cliched.
On reflection, the reason for that was that I was trying to limit myself to comparisons my narrator, Private Niko Han (second class), would use. As a farmer's boy and conscript on a far-away world a thousand years into the future, his frame of reference would be vastly different to my own; a city dweller now. I can't use the images that would come naturally to me.
Now, if I compared things to parts of his fictional world, I'd be left with another problem. This is a short-story. It is already longer than I'd like it to be (and I haven't finished it!). If I'm going to make comparisons to fictional things, the readers has got to know what those things are like. I mean, it'd be all very well for me to say "the Reaper's hit the ground like the shuttles landing outside my father's ranch", but the reader has no idea how those shuttles hit the ground. I mean, how good are the pilots? Are these soft landings? Hard?
Who knows? Not I, and I'm the writer. How could I expect the reader to know?
As far as I can see it, in order to use in-setting similes within a work of sci-fi or fantasy, you need to have already built up a substantial body of information in the reader's mind about that setting. Take swamp dragons in Terry Pratchett's work. If he says something is "like a swamp dragon," it means that it is prone to
explosive indigestion. In most fantasy novels, however, "dragon-like" it means that is is huge and fearsome.
You see? Comparisons are relative to setting.
So, how can one build imagery in a sci-fi or fantasy short story without assuming any knowlege on the reader's part?[/url]