The LTF setting was explicitly created to explore the question of how the Real World would respond to mysterious physical alterations. The basic premise is simple: What happens after a small group of people are inexplicably transformed? To this end, the LTF setting departs from mundane Reality in exactly two, and only two, ways: (a) The transformative Event itself, and (b) any consequences which follow from the Event. More than any other setting, LTF demands that authors take a good, hard look at the consequences that really would ensue if a transformation did occur, because there ain't no protagonist-friendly deus ex machinae to smooth over the rough spots for any Changeling (the media's term for transformed List-members). Fortunately, there also aren't any protagonist-hostile deus ex machinae to arbitrarily insert gratuitous rough spots into a Changeling's life.

The key to writing LTF is being ruthlessly honest with yourself. This setting is not for 'Mary Sue'-type wish-fulfillment fantasies, nor yet is it for everybody-hates-me-now-that-I'm-not-human tales of unrelieved persecution. What LTF demands is an objective look at the focus of your imagination, without glossing over the practical difficulties -- and also without inventing any unrealistic problems. For instance, an American who unexpectedly becomes a centaur might reasonably have trouble finding a farrier on short notice, but he might also qualify for US Government assistance as a result of Federal laws regarding disabled Americans.

With all that in mind, here are the guidelines to keep in mind when writing LTF stories:

1. Reality. Again (because it bears repeating): The LTF setting is indistinguishable from mundane Reality, except for the Event itself and any consequences thereof. This means no globe-spanning Secret Conspiracies; no magick; no perpetual motion machines; no visitations from extraterrestrial aliens; the only mythical creatures around (dragons, werewolves, etc) are those who were created in the Event; no 300-MPG carburetors rotting in clandestine Government warehouses; and so on, and so forth.
   If you happen to believe any of that exotic stuff actually is part of mundane Reality, no problem -- all you need do is pretend, for the purpose of writing LTF, that the exotic stuff isn't there. Since dyed-in-the-wool realists can suspend their disbelief as regards the flatly impossible Event, surely you can suspend yours as regards the proposition that whatever-it-is doesn't exist, right?
2. Inexplicability. By definition, the Event cannot be explained by any character within the LTF setting. Note that it's perfectly okay to speculate about the Event's causes, mechanisms, etc; you just don't get to establish that any particular speculation is Absolute Truth for the setting, is all.
3. Exclusivity. The Event affected people who were subscribed to the List at 'zero hour', and only those people; what's more, no one has yet managed to induce Event-type transformations in anyone who wasn't originally affected by the Event.
   This rule has excited more controversy than any other. It's here to stay, however, and the reasons why should be clear after a little thought. First, the LTF setting is not, nor was it ever intended to be, one in which anybody can transform. Thus, removing the 'exclusivity' aspect would destroy the setting's raison d'être. Second, given the sheer number of existing settings which are of the anybody-can-transform type, what point would there be in making LTF into yet another one? Absent the 'exclusivity' rule, what would distinguish LTF from any other setting -- why would anyone bother to write LTF when they could instead write TBP or WoC or whatever else? Third, the LTF setting is supposed to have exactly 1 (one) point of divergence from the Real World -- namely, the Event. You don't get to reset the date and time of the Challenger explosion, nor can you fiddle with the results of the 2000 US Presidential election, so why should you be able to tweak the specifics of when you subscribed to the List?
   All of which said, there are two loopholes for authors who ought not to have been affected by the Event, but nevertheless want to write 'fun with my new body' LTF stories anyway:
   • The setting's arbiter has declared that if it's okay to fudge a little on exactly when you became a List-member. As long as you, in the Real World, were a subscriber at any moment within a few weeks of 'zero hour', you can declare your avatar in the LTF setting to have been a subscriber at the right time.
   • The 'Lurker Loophole': At any given time, the vast majority of List-members are lurkers, i.e. people who receive and read List messages without posting anything. If you, yourself, were not a List-member at 'zero hour', you can always write about one of these lurkers who just happens to have your exact taste in transformations -- make that lurker yourself with the serial numbers filed off, as it were.
4. No superheroes. For each Changeling, the Event did its best to create their 'most imagined' form within the limits of mundane physical laws. This means that those List-members whose 'most imagined' forms actually have funky powers (magickal abilities, teleportation, flight, etc) were likely to be disappointed when the Event hit them. Most... but not all. The deciding factor for superhuman abilities is whether or not you bothered to envision a physical mechanism for the power(s) in question; sorry, but "hey, it's magick!" just doesn't pass muster.
   Suppose John Doe envisioned his 'most imagined' dragon-form as venting methane up his throat to be ignited by sparks from rocks rubbing together in his crop (i.e., a sort of 'pouch' in the neck), and Richard Roe's 'most imagined' dragon-form breathes fire just because he figured it's one of those things dragons do. Both would become dragons, but John would be able to play flamethrower (and would have to worry about such things as how quickly he uses up the methane in his gut), and Richard wouldn't. Similarly, while a number of List-members envisioned their 'most imagined' forms as shapeshifters, exactly 1 (one) Changeling has that power; this person actually envisioned a mundane physical mechanism to explain it (operational restrictions included), which the others did not. If you aren't sure, ask the setting's arbiter for a ruling.
5. You asked for it, and by God you're going to get it. The Event used each Changeling's concept of their 'most imagined' form as the blueprint for their transformation. Thus, two Changelings whose 'most imagined' forms were nominally the same (both of them dragons or whatever) might have ended up with quite different post-Event bodies, depending on the specifics of each person's concept. Given two List-members whose 'most imagined' forms were both werewolves, one might have envisioned his werewolf-self as an instinct-driven engine of destruction, a constant danger to himself and others; the other might have had a more benevolent, Teen Wolf-type concept of lycanthropy in mind. As Changelings, both of them would have ended up exactly as they had imagined.
   Note that a List-member's 'most imagined' form is not necessarily his favorite one, nor even the one he himself would most prefer to have, given his druthers. It isn't at all unlikely that a List-member's 'most imagined' form would be his personal favorite, of course; it just isn't mandatory that it be so. If John Doe spent lots of time writing about post-operative male-to-female transsexuals, but was not himself dissatisfied with his own gender, he would have gotten a real big surprise when the Event worked him over.
6. No killing. Every Changeling is a biologically viable creature, perfectly adapted to the appropriate environment(s). A List-member in Montana whose 'most imagined' form was an ocean-dwelling (and exclusively water-breathing) merman would have major problems when the Event zapped him, but he'd be okay if he could manage to immerse himself in salt water before he asphyxiated. Those List-members whose 'most imagined' forms were inanimate (i.e. robots, teddy bears, etc) would, as Changelings, end up with living bodies that were nevertheless as close to their imaginings as physically possible.