Write What You Know... Or I made an 'oopsie'
I have one simple rule of writing fanfiction: Never write in a fandom until you have watched as much as you can (preferably from every season) and/or otherwise have researched the show--visiting websites, asking questions, reading as many descriptions of missed eps as you can find. Obviously, this is not a rule everyone follows. I have no idea how many intros I've read that say something like "I've only seen three eps of this show, but I just had to write this." I've even seen: "Well, I've never actually seen this show, but I looked at pics and read some other people's stories." HUH?? How can you write about characters that you've never heard speak [or read their words in closed captions] or seen move? How can you possibly know their mannerisms and how they relate to each other?
I suspect that a lot of "fanon", or fan canon, comes about in this way. People read stories and, whether they do watch the show closely or not, begin to lose sight of where certain info comes from, the show or the fic. The line becomes so blurred that something a fan writer came up with gets taken as gospel. (There are also other aspects of fanon and how it comes about, but since they don't really relate to this topic, we'll tiptoe quietly past and hope we don't wake them. ;-)
OBLIGATORY DISCLAIMER: You do not have to have every episode memorized to write fic--especially long running shows that have so much information to remember about a lot of characters (XF, HL, and Homicide come to mind). BUT other research to supplement the eps you *have* seen is really important. Some shows have a LOT of *factual* info available on the web if you just look for it, and ask questions of a long time fan or two. Make sure you know the people you're writing about. I know someone who wrote some kick-ass fic this way and got the characters' voices down really well (she has since gotten every single ep of that show on tape, too!), so it *can* be done. But this is the exception NOT the rule. It takes a lot of hard work to pull it off or a truckload of talent, depending which you've got more of at your disposal. And a certain amount of fearlessness doesn't hurt much either. ;-)
So do I have a point in all this? Yes, surprisingly enough. I broke my own rule. There... I said it and I feel better for it. Slightly. The weird thing is that I still really like the story, even though a fairly big assumption that I made from a few remarks both on the show and in the episode guides was proven wrong. After a new ep aired and shot my theory all to hell, I went back and watched the eps I had on tape and saw that I had simply missed a brief scene that would have saved me from making the mistake I did. At the time I wrote the story, I'd seen about 8 eps (I'm unclear on the number because I didn't tape the first few I watched) and I just don't think they were enough. [I've since been told that I'm being too hard on myself about this. Which may be true, because I am definitely my own worst critic. There's nothing a flamer could say to me that I haven't already said to/about myself at some point.]
But you know what? I'd do it again if I felt as moved to write as I did that time. I would watch my taped eps a bit more closely, but I'd definitely do it again, because when a character really starts speaking to you, it's very hard to ignore. When you get that voice in your head, it has to come out sometime...somewhere. Some people call them Muses, some call them plotbunnies, and I suspect that some could call them schizophrenic auditory hallucinations, but whatever they are, the compulsion to write them is very strong.
Two of my current favorite shows are Buffy the Vampire Slayer and Angel (partly for the simple reason that they're both still on the air and have new eps occasionally). I haven't written any fic for two reasons. The main one is that none of the characters have 'spoken' to me. Whether that's an identification issue or a 'captured the voice' issue, I'm not sure. The other reason I haven't felt moved to write is that I only started watching BtVS in the spring of '99, so all I've seen at this point is a small part of Season 3 and all of S 4 (and whatever reruns they showed over the summer). My favorite character is Spike, but I only have very second hand knowledge of his history before he showed up in The Harsh Light of Day looking for the Gem of Amarra, so although I'd love to write him, I don't feel qualified. And frankly, the pro novels have left me more confused on the details than ever. The show says that Angel made Spike, but at least one of the books I read said that Drusilla made him. I'm not gonna stress over it or anything, but I hate it when TPTB can't get and/or keep their facts straight. [After I wrote this, this very subject came up on an Angel list I'm on. The consensus seemed to be that Joss just messed up the math. <sigh> Whatever.]
Anyway, I guess my ultimate point is that it irritates me to no end when people write in fandoms that they haven't properly researched, and yet I can't do a thing to stop them. So basically, there's two things that I've learned the hard way: 1) You can't ignore the Muse...but 2) Always remember the 7 P's: Proper Prior Preparation Prevents Piss-Poor Performance. (I know that's not how Benton Fraser said it, but I like this version better. ;-)