Fanfiction, for those who don't know, is basically the practice of writing your own stories set in another author's world and/or using another author's character(s). It's a surprisingly common activity; or perhaps I should say, it's an unsurprisingly common response to reading a fun and well-told story: "I wish I could be there, doing that."
(The comic Girl Genius includes a humorous interlude which focuses on the creation of fan fiction by a character from the world of the comic. The interlude begins here, and runs about seven pages; it is entirely separate from the main storyline, so reading it will not spoil anything from the rest of the comic. By the way, if you aren't already reading Girl Genius, you should be - it's exceptionally well done. Or, do the authors a favor and buy yourself a copy; it's available as a printed comic book, too.)
Like any other sort of writing, fan fiction can be done spectacularly well, hideously poorly, or anywhere in between. It sometimes gets a bad reputation, usually owing to one of three reasons:
- It's fundamentally derivative. That is, it is based on someone else's work (by definition).
- A lot of fanfiction is very badly written - poor grammar, frequent spelling errors, and misused words abound.
- Fanfictions frequently borrow characters created by other authors, and use them in ways that are inappropriate, and sometimes deeply disturbing.
I want to stop and elaborate on that last item for a moment. I once read (as part of a class on Science Fiction) a fanfic in which two characters from the original Star Trek series were trapped on an alien planet. This was not, if you'll recall, an uncommon occurrence. In this case, however, the two characters were Spock, the half-Vulcan who almost never showed emotion, and "Bones" McCoy, who was perpetually angry at Spock's failure to act more human; and the event which trapped them was "psychic storm" which prevented them from beaming back to the ship and threatened to burn out their minds. The climax of the story had them huddled together, with Spock performing a Mind Meld to get them through the night - a strange sort of intimacy for these very different, somewhat antagonistic men. The story was well-written, and very true to the characters, but it was also exploring psychological territory that the original TV show would never have approached. I suspect that, for the author of the fanfic, that was precisely the point.
There are a great many fanfics in which the author has inserted an "idealized Me" character (often referred to as a Mary Sue) into an existing series. These stories tend, by their nature, to put the author's Id on display, often with disturbing results. As an example - which, for the sake of your sanity, dear readers, I will not link to - I offer a fanfic in which a teenage girl was accepted to Hogwarts. She was (unsurprisingly) exotic and attractive, and quickly turned most of the students on to her favorite bands and her goth style of dress. Where it gets disturbing is the bit where, in very short order, she is sleeping with Harry Potter, Draco Malfoy, and Professor Snape - and suffering great angst over the question of how she could possibly choose between them.
Despite these criticism, there are a great many people writing fanfics, and some of them are actually quite well-written (which, for me, generally includes being true to the source material).
My own experience with Fan Fiction is, as far as I can tell, a bit different from most. I first stumbled onto it when I was looking for information on the Bordertown series of books. Bordertown is a "shared world" anthology (or series of anthologies, really). In other words, different authors all took the same setting and wrote their own stories in it. (The series also spawned at least three full-length novels, from authors who wanted to do more with their characters.) So, naturally, the group that I had stumbled onto did the same: took the setting, and wrote their own stories with their own characters. This differs from the usual run of fanfiction mainly because the "original" characters are left almost entirely alone.
Later, I stumbled onto The Grey Tower, which is set in the world of Robert Jordan's Wheel of Time books. This was, again, entirely accidental; I was doing a search for a particular type of Japanese polearm. The Grey Tower, despite being set in a world created by a single author in a (quite long and excruciatingly detailed) ongoing series, uses much the same approach as the Bordertown group: everyone has to create their own characters - you can't use one from the books - and Grey Tower events must always take place "offstage" in regards to the original series. Moreover, characters and events have to be true to the spirit of the series; you can't introduce psychic powers, or a new system of magic, or that sort of thing.
So, granting that my experience with (and practice of) fan fiction is a bit unusual, I tend to think that it can actually be quite good as writing practice. That's particularly true if you're looking to polish your style a bit before starting on your own projects. Here's the thing:
To keep your setting internally consistent, you have to pay attention to the details. This is true regardless of whether you're inventing your own world or borrowing someone else's. In order to stay true to the original author's work, a fan fiction writer has to make a fairly close reading of the source material, and then do some careful analysis of how things work, and what does and doesn't fit in that setting. That same sort of thinking - How do these things work? What can we do with this element? How does this ability change the way our society works? - is quite valuable when you sit down to create your own worlds.
In my own fan faction, I do not use published characters. When I do use other people's characters, they are always from people I know, with whom I can consult to make sure I get the details and the behaviors right. This is, again, good practice for characterization.
Sites like The Grey Tower actually offer classes to help with some of these elements. They have an introductory class, which includes several lessons designed to help you explore your character. Other classes, such as Writing Combat, address other areas of writing. You can also get feedback on your writing (sometimes even if you don't want to hear it).
Now, obviously not all authors of fan fiction are going to put this much thought, or this kind of thinking, into their work. For the ones who do, though, I think that writing fanfics can be a good way to improve one's writing in general. Most people are eventually going to want to move on to creating their own worlds and their own characters, but spending some time really exploring someone else's world is not a bad way to start.