I want to talk a bit about writing outside my experience. I am, for all intensive purposes, a white cis straight lady (I mean, I'm Jewish and possible asexual, but you get the drift). As such, writing diverse characters is something that doesn't come natural to me. I have to work at it.
When I first started writing POC characters, they were so kind of arbitrarily. As much as I like my story Malai, the protagonist could really be any race. I sort of made her black for diversity's sake.
But as my writing progressed, I tried to make race a more real part of my POC character's lives . Whether it's my character Esther in my webcomic, who is a black girl going to a virtually all white school, or it's Kamon from my comic Safe, a Thai immigrant who is dealing with Trump's America. I want these characters to be more fleshed out than just me making them have a non white skin tone with the Photoshop paint bucket tool.
The way I have tried to write these characters more authentically is to ask people outside of my race about them. Having a very diverse group of friends has been helpful for that. My friend Salakjit really helped me with finding Kamon's voice. She isn't really like him, she came to NYC from Thailand as a kid and knows who Oasis is, and her english is very good. But she has told me about how she navigated the election as a both an East Asian woman and as an immigrant with an accent. She also was the one who told me that the song for the karaoke scene should be Oasis (She loves karaoke)- a classic karaoke song that Kamon could conceivably have not heard in Thailand.
This isn't just about race either. I tend to write of queer women characters; mostly because it's an excuse to write more women characters period. That, and I do not know how to write for straight guys, and don't really care to learn (they get enough representation already). So I have a few queer people I ask to look at my work so the characters seem more real. Tillie, who I did the Planned Parenthood comic with, is my go to reader for that. Not only do I respect her as a cartoonist, but I've heard her talk about how straight people often suck at writing queer characters. So I run things by her so I, y'know, don't do that.
And this can be done for lighter topics too. Not only did I ask my friend Christine to sign off on Esther from my webcomic (the character is based off Christine in a lot of ways), but I also ask her for astrology help all the time. For example, in Wasted, Christine told me that the protagonist was a Gemini and helped me write her horoscope. Or with the comic I'm going to be doing for Square City's next collaborative project (I talk about that here), the story is about a bartender and a customer falling in love. That meant that there'd be a lot alcohol in it, and I don't drink. So I asked my hipster (-esque, he's not a full blown hipster) brother, who knows about drinking culture questions like, "What kind of alcohol would a sweet bisexual lawyer take a shot of as a shot of as 'liquid courage?" Did you know cool kids drink Manhattans? That's what he told me. Fucking gross, but fine!
I recommend having a lot of friends that are very different from you to learn about this stuff from. Not only because it makes your writing better, but because it also makes you a more empathetic person.