Regarding POC characters *starts to laugh*. I mostly only write as women of color characters. I struggle trying to remember to include and represent white characters. 
It used to be quite the opposite for me because, as a teenager, I thought it was customary to write white characters since that's mostly what I read and saw on the screen.
Even though I'm a bi-racial (black/white) person myself!
[i]Side note: I identify most of the time as black--except when people ask if I'm Asian or Latino, I then tell them no, I'm mixed/bi-racial (black/white).[/i]
So then I went to a convention session one summer in High School that spoke about the lack of representation of POC in film, books, TV, and comics and was like... well, [i]Holy Shit[/i]. 
[b]I'm black, and I'm adding to this problem![/b]
I now strive to find fiction/fantasy books about black female protagonists and other WOC (women of color) as the protagonist. 
And since I want to read/watch more about them, I mostly write WOC characters to help get more "coverage" out there. LOL.
Now my goal is to get educated more and consume more entertainment about LGBTQ+ characters.

On the topic LGBTQ+ characters, I've only enjoyed writing as asexual or gay characters (I mean other than straight). Bi-sexual and pan-sexual characters are hard for me to write well. But I understand it shouldn't be since, like others have said above this post--WE are ALL human in the end. And I know there are even more different orientations, but I still need to learn more about them before writing tales from their POV. Like I said I'm open to being educated more. Regarding trans characters, I've only written as one FTM trans character in the past, but even then, I barely ever mentioned their 'trans' identity as it wasn't imperative to the story... but then I felt like I was doing the whole 'hiding/closeting' thing. So, unfortunately, I started to avoid that situation instead of learning more.