On the topic of fan fiction
My previous post, way back in the mists of time, was a short specimin of fan fiction. Admittedly, not the best that is out there, but that is neither here nor there. Attempting to write in this art form gives one a perspective that cannot be attained merely by reading such work, because you're locked in to a universe of someone else's devising, working with characters whose personalities you can't alter too much (and preferably not at all), if you're to avoid writing what is sometimes termed a Mary Sue.
A Mary Sue is a type of fan fiction that is basically personal fantasy, written with no particular artistic merit because that's not their function. It's nothing to sneeze at, people have made fortunes writing Mary Sues. Entire publishing lines exist solely to produce them for the mass market, although it's not always obvious what they're a take-off of. No pun intended. The readers and writers of such works deserve respect for their choice of genre, but they're not looked upon highly amongst fan fiction writers, as a rule.
A much more common fault, and one I'm guilty of a great deal, is the contrived plot. You've got a scene in mind and the rest of the story really exists just to justify including it. It's a variant of the above theme and should really get similar disapproval, but it tends to get a lot more care and attention in the writing. The plausibility of the plot devices determine the plausibility of the objective. The characters also tend to be less objectified, as it's about their success rather than their conquest. Now, that's not always true, but even the worst-written fanfics of this kind I've personally read (and some were truly dreadful) have had the redeeming quality of the author making an effort to write a story.
To all English professors and professional authors on SteemIt, yes, I know, I take a very different tack when it comes to writing than is conventional. Difference in perspective, though, is very different from being wrong.
To me, literary works divide into three basic categories - objective-driven (as detailed above), character-driven (the staple of easy reading) and universe-driven (the most challenging form).
Objective-driven I've covered, character-driven you're familiar with if you have ever read a novel, which leaves this last form. Universe-driven writing starts with the world/universe, the story becomes what Reality TV never was - "live footage" of what happens to the people in it.
J. R. R. Tolkien wrote universe-driven fantasy. When I asked him at a WorldCon, Terry Brookes stated he partially used that technique. I'm fairly confident Katharine Kerr has made use of it, too. All brilliant writers. In this form, the universe hangs together and is believable in its own right. It's a sustainable "sub-creation" for which suspension of disbelief is unnecessary, in Tolkien's terms.
It's also a form that some authors have stated flat-out can't exist, that stories don't work that way, that anyone who claims suspension of disbelief is unnecessary is flat-out lying or deluded. These are the people whose toes I tread on regularly on this topic, because I don't think dismissing categories is helpful in understanding the written word, particularly when it feels more like an overemotional reaction to something that's about as relevant to their own world and thoughts as the weather forecast on Jupiter.
Universe-centric writing really comes to the fore when the writer is using a universe that already "exists" but characters that don't. Stories set in the "Elite" (as in Ian Bell/David Braben computer game) universe fit in this category. Deviating from the universe makes for a bothersome story because the universe is known and beloved to multiple generations of fans. Every last nit has been picked a dozen times or more. Only the Big Three (Star Wars, Star Trek and Doctor Who) have received more scrutiny and the discontinuities are such in those as to allow near-infinite freedom of interpretation.
Simulated universes (more on that another time) are a different matter. The differences exist solely in the interpretation of non-canonical padding.
However, precisely because you're re-using the same universe and this style of writing is studiously avoided (unless you're autistic, like myself, when it's the only sort of fiction that can be read comfortably), this tends to be where fan fiction divides into the absolutely brilliant and the absolutely dross, with nothing much in the middle. The learning curve is steep and fans can be ruthless, so you're a natural, a very fast learner (a genius by any other name) or prey. It's a tough ecosystem.