I’m going to use “progressive characters” as a catch all term for “POC, LGBT+, and other minority characters.”

I’ve written (nearly) everything under the sun from a bisexual Chinese woman to her adopted Indian daughter to a Jamaican news reporter. And I’m happy to say that regardless of what you write, you’ll do the best job if you stick to one simple rule:

Write your progressive characters the exact same way you would your normal characters.

I feel like a lot of progressive characters make this mistake where they are so focused on being non-hetrosexual/white/etc that they forget to be a compelling character with motivations and aspirations that extend past their preferences/skin. 

I once had a neighbor that happened to be a lesbian, but you wouldn’t know that just talking to her. It took her a few weeks to warm up to my family and I. That was when she felt comfortable talking to us about the tragic death of her wife. Compare that to your average homosexual RP character who makes sure everyone knows how gay they are seconds after meeting them. That's also a surefire way to make your character look like a sex addict, which isn't too flattering.  

While it’s good to learn about cultures, it only really helps the character if it’s important to them. As an example, there [i]are[/i] lots of Chinese-Americans who are still faithful to the Chinese way of life. But just as many have embraced America’s culture and couldn't care less about Chinese customs. Even if they did, most of these people aren’t going to drop Chinese sayings into casual everyday speech with strangers. It feels pretentious and might even be a little embarrassing for all involved. I’ve personally seen Japanese-American characters who were born and raised in America, yet for some reason they add Japanese honorifics to their otherwise perfect English. It's all reminiscent of lazy translations done in anime. You could argue that their parents taught them to speak this way, but I have yet to hear anyone talk like this in real life. Point is, while culture can be a great thing to learn, over-applying it can turn a character into something that is both generic and bordering on racist. I think that’s something we all want to avoid.

I’d also like to add that you should absolutely bury your gays if the story calls for it. Sure, we’re all familiar with the tropes. How the black dude dies first and what not. But if your story is one that is rife with despair and sadness, excluding progressive characters from the looming threat of death is a disservice to everyone. Making your chosen minority/etc safe or otherwise infallible in a story is just as bad as indiscriminately killing them off. A writer should not be held at gunpoint by their characters. 

Ultimately, the less special treatment you give your progressive characters, the better.

If you need to research something, do some reading on the area where they grew up, or the time period if that makes more sense. Learn about their job and what type of skills they may have. Read reports on what happens to people who go through their extraordinary circumstances. That information will serve you well. But also note that this kind of stuff is good for any character you choose to make, not just your progressive ones. I just spent a few hours reading about Kharadron Overlords so that I could play one in my brother's tabletop game.