Writing fan fiction is not the same as writing regular fiction, even for professional fanfic writers (think the books based off TV shows). Fanfic in general is very different for two very specific reasons.
Fanfic authors have complete editorial control over their work. This does not happen in the publishing world. Both the literary agent, and the publisher who eventually picks up the novel will have much of the editorial control. Also, titles are very often changed.
Fanfic authors can’t make money off their work. We’re paid in reviews, not cash. This is great for the people reading, but I don’t imagine many of my fellow writers would turn down the opportunity to be paid for their work.
This applies to professional fanfic writers as well. These are the people who write books for Criminal Minds, Star Trek, Buffy TVS, Supernatural, Glee, CSI, Dune, Battlestar Galatica and what I imagine is many, many others. They get to make money, and are subject to the same rules as the rest of the publishing world. A side note on these to enthusiastic writers, you do not write a fanfic book and send it to a publisher/literary agent. If a network wants someone to write novels based on their show, they’ll pick an already established author and commission them to do it.
Moving onto the writing. The primary differences in writing fanfic versus original fiction are that you’ve already have characters, setting, and generally tone set for you. Tone and setting are flexible to an extent, but the characters are the reason you’re writing the story in the first place. You want to keep those characters, though you do have the freedom to choose which to focus on in your writing and how you want to develop them.
Already having characters removes a considerable chunk of the work you have to do, and if you don’t believe that, try writing a novel. I’ve done it, and trust me, developing characters is not easy and takes a considerable amount of work. By having characters already written, you know what they look like, what they sound like, how they act, nervous tics and odd mannerisms, and an entire history on which to build. Often you have a few seasons of a show, or several books or comics that have given you a clear, very distinct impression and an opportunity to sort to integrate that characters in your head. With original work, you’re starting fresh, and it’s hard to keep track of every character in a book, and make all your central players stand-out when you haven’t been with them very long.
The flipside of that though, is that you have to know someone else’s characters and do your best to stay true to those characters. I reread the X Files novels a few years ago (yes, I’m a nerd), and I was disappointed to realize that that author could have been writing about anyone. It said Mulder and Scully, but there was very little distinct about the characters in the novel, and certainly nothing that said they were Mulder and Scully. That is your challenge as a fanfic writer, to get to know someone else’s characters so well you can put them to paper in your own voice and words.
Like I said, setting can be flexible depending on the show, book or comic. Obviously if you’re writing for Star Wars, you need to set it an their universe, but you can pick which planet and even what location on which planet. In some series, like Criminal Minds, the X Files and Supernatural, the characters often travel, so you’ve got a lot of freedom. In other series, like Grey’s Anatomy, Law & Order, and Charmed, the location is more static, and you need to have good reason to move the story out of their city.
Tone is a little less concrete, and it often changes (and should) even within the show, book or comic, but there’s still sort of a central tone, a general feeling to it that remains the same throughout. Think of the feel of Bones or NCIS versus that of Criminal Minds or Law & Order. The former two shows have more of a fun, humorous tone to them, and while the latter both have moments of humor, they’re darker and more serious. Likewise, Bones and NCIS both have their darker, more serious moments. Fanfic writers have to stay true to this tone. Of course, like in the original work, the tone should be fluid in a story, but still hold to that overall feel.
What do you think are the major differences with fanfic and original fic? What do you think are strengths and weaknesses of fanfic?