That's so helpful, right? Good to know?
Here's what I can tell you about how I learned voice and how I found and am still finding my own.
Voice starts with listening.
Ever since I've been able to read, I've noticed that the voice of a text gets in my head and I start thinking in the voice of whatever I'm reading. For me, reading is the first act of listening.
I don't know that this is anything to brag about, but I am a mockingbird when it comes to voice. I can imitate just about anything. This has gotten me many a freelance job in an industry where matching your own tune seamlessly to the rest of the songbirds is one of the best skills you can have.
As with every other element of good writing, you learn voice by reading.
In my formal historical training, I learned to listen to documents, to catch the beat of a given time. It takes a while, at first, to read your way in, to realize that everything distilled for you before was filtered through lenses that drowned out the original voices, to understand that you are in a new place where you don't know the language and you have to listen hard to learn it. Research is the second act of listening.
My fiction has always begun with a voice in my head. The first step of writing is listening to the voice, sometimes for years, and hearing what it wants to say and how it wants to say it. A few years ago, people in the world of literature were having a delightful tempest in a teapot over point-of-view and tense and why an author would choose one and not the other. For me, it's never been an active choice. I've always gone with however the narrative voice came to me, for better or worse. Sometimes it's first person, sometimes third. Sometimes past tense, sometimes present. Good books are written in all of them—I thought the whole argument very silly.
I've never once worried--or perhaps, known how to worry--about whether I'm writing in a Middle Grade voice, or a YA voice, or an adult voice. People are not the same just because they are the same age. The best I can do is to listen to the characters. But it's possible I have an advantage here because I don't write contemporary fiction (I am nowhere near cool enough), so I don't have to keep up with exactly what the kids are saying these days.
So I guess listening is the third act of listening.
Voice is hard to explain, but if you're struggling with it, the best advice I have is to listen.