Trans people are a big thing these days in equality circles. People are asking what they can do to help the trans cause. Quite simply, the most important thing cis people can do for the trans community right now is to accept us as fully human; not as something to be gawped at and whispered over, not as a clever metaphor with which to discuss gender, but as ordinary people just like you. For cis writers, that means putting us in their stories.
I reject the idea that trans characters should only be written by trans people because cis folk are bound to get it wrong. While there are some really fine trans writers, there simply aren't enough of us in the world to do what is needed. We have to be part of all fiction, not just fiction that we write ourselves.
We are in some SF. For example, years ago Sandra McDonald in her Diana Comet stories recognized that trans characters can be heroic and have adventures. Another McDonald, Ian, has worked really hard. He did the transition narrative in River of Gods, but has since moved on. Characters such as Edson in Brasyl and Lucasinho in Luna: New Moon are effortlessly and naturally gender-fluid (and bisexual to boot). Kieron Gillen seems to have adopted a policy of giving at least one character in every comic he writes a trans backstory, while mostly not making an issue of it in their current lives. Elizabeth Bear's Jacob's Ladder trilogy asks some important questions about gender and individuality without making the trans characters ciphers in service to the argument. Alison Goodman allowed a trans woman a powerful role as a senior imperial concubine in Eon.
I am looking forward to new books from Paul Cornell, Cory Doctorow, and David Barnett. All of them will, I understand, have trans supporting characters in them. What I'd really like to see, though, is more stories in which trans characters take the lead role, rather than being a supporting character.
Of course, what works for me may not work for other people. And while authors, for the most part, have the best of intentions, sometimes their efforts at representation may not always be well done. Trans people are comparatively rare in society, and are still widely misunderstood, so what we actually get might be the trans equivalent of the tragic gay best friend who dies at the end of the book, or worse. So what I want to do is to suggest some things for cis writers to think about that may help them to avoid such missteps.
The obvious thing to do is to talk to trans people. There are some who are tired of doing trans 101 for their cis colleagues, but many of us are willing to help. I have spoken to several different authors so far this year. However, one thing I always tell them is not to assume that I am typical. The trans community is highly diverse. The experiences of trans men can be very different to those of trans women. The feelings of someone who is gender-fluid—that is, tends to switch their gender performance on a regular basis—is very different from someone who has a deep-seated need to transition permanently from one binary gender to another.
One solution to this, as with all LGBT characters, is to have more than one. Gone are the days when people like Christine Jorgensen or Jan Morris suffered in lonely isolation. Even the pioneering British trans woman, April Ashley, had a bunch of trans friends. Several of the girls she worked with at the Carousel Theatre in Paris went on to have gender reassignment once their colleague, Coccinelle, came back from Casablanca showing off her brand new vagina. Equally, however, getting a bunch of very different trans people right can be challenging. It might be easier to get a good understanding of one sub-group, and just be careful to make clear that they don't stand for all trans people.
Things to avoid
There are things that you should definitely avoid. One is doing a shock reveal. That sort of thing has worked very well in other areas such as in discussions of race, where it may help promote acceptance because the readers have been primed to like that character. With trans people it is different, because so much of the transphobic narrative is bound up with trans people being "deceivers."
A major problem that trans people face is that so many cis people think that gender is somehow fixed at birth. Thus, they say, even though I live happily as a woman, and identify strongly as a woman, to them I am "really" a man who is "disguised" as a woman. Cis men often use this as an excuse for murdering trans women, claiming that they had been tricked into "becoming gay" because they found one of us sexually attractive. Radical feminists claim that trans women are men who disguise themselves as women in order to sneak into women's bathrooms and commit rape.
Because of this, if you do a shock reveal in your book, you are playing into this narrative of deception. You are encouraging your readers to think that trans people are somehow out to trick them. Please don't do that. It is an idea that gets us killed.
Something else I would really like authors to do is stop focusing on the process of transition. I know this is hard. The actual fact of changing from one gender role to another is the thing that most fascinates cis people about trans folks. There is also a temptation to see transition as a moment of cure, or release, which has a positive dramatic payoff. For trans people, however, transition is a fairly unpleasant experience. You are essentially going through puberty again, with all of the emotional turmoil that entails. People you know and love are having a bad time adjusting to the apparent "new" you. It isn't something we want to read about. If it is the only thing we ever read about it shows us that we are still seen as a freak show, not as the ordinary people we mostly long to be.
Oh, and don't do that thing where, for the purposes of the plot, a trans character has to go back to presenting as their birth gender at some point. I know it is tempting, but all you are doing in such cases is reinforcing the reader's idea that the trans character is "really" a person of their birth gender, not the person that they claim to be.
If you want to blow up traditional notions of gender, use a gender-fluid or otherwise non-binary person to do it, not someone for whom it is incredibly important that they should not have to present as their birth gender.
The cis gaze
There is a real issue with regard to who you are writing for. There is such a thing as "cis gaze"; that is, a book can be written because cis people are fascinated by trans people. They want to see us doing those weird trans things that they think we do. Or they want to see us as victims that they can feel sorry for and rescue.
Back in the 1990s when Neil Gaiman wrote the Sandman story A Game of You, there was a desperate need for cis people to understand just how badly trans people are treated. Neil did that very effectively, and gained a lot of sympathy for trans people as a result. But the world has changed now and trans people no longer expect to be treated really badly. What we need from fiction is to be treated as equal members of society.
What I'm looking for is books that are not written from the cis gaze. I want books that are happy to accept trans people as people who can do all sorts of things in life, not just make theoretical points about gender by transitioning from one to the other. Or suffer tragically because they are not accepted by society.
The key to this, as with writing any character, is to get inside their heads and respect them for who they are. So suppose you are writing a transsexual woman. Don't see her as a man who wants to be a woman, or a man pretending to be a woman; see her as a woman who may suffer discrimination from people who don't think she is woman enough. Think of her as being in a similar position to someone who is told that she's not a "real" woman because she's a lesbian, or because she doesn't want, or can't have, children.
Other characters may see her in a different way, of course. No one is asking you to write a world in which discrimination doesn't exist. But allow your trans character to think of herself as a real trans woman does, and think about how she would feel about the way cis people tend to view her.
I'm less confident giving specific ideas as to how to write trans guys, or non-binary people, because I'm not sure I understand them that much better than cis people do. I'd want to sit down and talk with them about their experiences, and maybe read stuff they have written about people like them.
A final thought
You should also think about how trans people fit into society. There is ample evidence that many societies around the world, and throughout human history, had a much more relaxed attitude to gender variance than we do in Western society today. If you are creating a fantasy world, it doesn't have to be deeply transphobic. In fact if it isn't based on a fairly modern Christian or Islamic view of the world then it would be odd if it was. Every early Christendom and Islam were more accepting than we are today.
Of course the concept of the homosexual is a modern invention. So is the sharp distinction between sexuality and gender identity. But if you want to write a story based on a realistic portrayal of ancient societies you should probably make your characters less neurotic about gender and sexuality than modern people are.