I started writing a fantasy novel last week and it’s been going pretty well so far by following the tropes. I’m hinting at some social problems here and there. Elves and humans are both pretty self-satisfied that they’re socially superior to orcs and goblins (except some actually have an inkling that maybe they’re not, maybe the orcs might have superior small-scale social organization, for example).
There’s two kinds of worldbuilding in fiction writing: The kind that happens at leisure, before the project begins, and the kind that happens ad-hoc, on a tight deadline, during the project. In the case of this novel, because I didn’t have an inkling I was going to write it before November began, I’m running on 100% the ad-hoc kind of worldbuilding.
When I start a project on a tight deadline, it’s occasionally useful for me to keep a notepad beside my computer and jot down worldbuilding notes for future use, because I’m going to be referring back to them on a fairly constant basis (especially because I haven’t been developing this world for months or years the way I have been Aquarius Ascendant; my worldbuilding for this novel began when I started writing).
It’s also good to keep some builder notes around that don’t show up in your story yet – this fantasy world’s human beings, for example, are the distant descendants of earth humans from our future, thrown back in time through a cataclysm in deep space. There are hints in the setting of this past, and yet what few relics of Earth technology remain are inoperable, because they depend on power sources that decayed to the point of uselessness millennia ago.
When time doesn’t allow you to do detailed worldbuilding, something falls into the gaps, and one of the big gaps in my novel so far is the magic system (which is ironic because one of the chapters centers around one of the characters doing a big powerful ritual to bind her new sword). So far I have the general idea that lasting magic requires ritual but blasting power around on the battlefield can be done on an ad-hoc basis and possibly (not certainly) even by untrained people, but I haven’t sat down and designed this explicitly (it will probably get worked out in the revision process, though). I also haven’t designed military tactics yet, though they’ve clawed back at least enough technology to have cannon (I’m pretty sure there are flintlock firearms as well).
On the fly worldbuilding has its issues. You have to watch out doubly much for unconsciously absorbed attitudes about race and gender because there’s not as much room to write those out when you’re starting from a blank slate and building a world in the space of 50-60 thousand words. And you can write yourself into a corner 30,000 words in that you didn’t realize you’d written 20,000 words ago.