Progress is usually a good thing, especially in terms of LGBTQ characters in media. It's no lie that media has made a lot of progress with the inclusion of LGBTQ characters in their properties in the last 20 years. But sometimes that progress isn't always a good thing. Just because a movie includes a gay character does not mean that the character is a positive representation of the community. Some of the worst offenders, though, are writers of transgender characters.
Although there are many problems with LGB characters (who almost always ending up as stereotypes), transgender characters tend to get hit the hardest. This may be due to the fact that the people writing these characters are cisgender (people who identify with the gender they are assigned at birth) and do not understand the true experience of being transgender. It's also due in part to the history of violence and oppression trans people have suffered, and it's hard for people to grow out of that.
Because of this history of violence and oppression, there are a few things that writers should never do when writing trans characters. The first, and possibly most important, is to never use transphobic slurs in regards to the character, or even in general. Especially when describing the character, never use any slurs as most have a history of derogatory connotations. Even in situations where writing about a trans character being bullied and having slurs thrown at them, it's important to be careful as it's very close to reality and can be triggering for them.
In tandem with the use of slurs is the graphic depiction of violence against trans people in media, especially trans women. This is important to avoid for it can also be extremely triggering considering most trans people go through violence on a daily basis. Because of this, they don't want to see it when they're watching their favorite TV show.
Another reason that's less obvious is the act of trans people using their "deadname". This term refers to the use of a transgender person's assigned name at birth. While this may not seem like an act of aggression, using someone's deadname hurts many people within the transgender community. When done on purpose, using someone's deadname can be as harmful as a slur, as it basically ignores that person's existence, since that is not who they are or ever were. Using a trans person's dead name is a slap in the face to that person, and it should not be used in most circumstances.
While the list could go on and on, my last suggestion on writing trans characters in media hits on an ongoing phenomenon in Hollywood happening currently. That is the casting of cisgender actors in transgender roles. We've seen most recently with Jared Leto in "Dallas Buyers Club" and Eddie Redmayne in "The Danish Girl", and TV shows such as "Transparent".
Even if the writing follows all the tips I mentioned previously, and treats the transgender community with the most respect possible, the fact that these movies decided to cast cisgender men in the roles of transgender women is a big "screw you" to trans people everywhere. These movies tell trans women that they are not real women, simply men dressed up as women. It also doesn't give actual trans women the chance to represent themselves on the screen.
If we're going to be making progress in terms of LBGTQ representation, then we need to do it right. Trans people tend to get the worst treatment of all, which isn't fair to them as they are just as valid as any other person in the LGBTQ community. Obviously, these are not the only ways in which to write a trans character in a positive light, but these are the most prominent and important, in my eyes.