How can you put in a non-binary character (person using pronouns They/Them) into a story without confusing the audience about if you’re talking about a group or the person?
There aren’t really any special tricks for singular they. Just do what you would do for any pronoun, and be on the lookout for plural things you mention in the story that “they” could refer to instead. All pronouns are based on context, so this is similar to if you have two women or two men in a scene and you have to make sure readers know which one you’re talking about. You may need to use names a little more often that you would otherwise, change the subject or object of the sentence, or modify when you use the name as opposed to when you use the pronoun.
The only thing that I’ve found to be different with singular they is that the reference needs to be extra clear the first time you use the pronoun for a character. Readers just need more help making that association for the first time.
If you’d like to see an example, in my short story, Biological Intelligence, the main character uses singular they (as does every other character besides BI, but there aren’t many characters). In the opening, I used their name five times before I brought in their pronoun for the first time in the second paragraph. I did this to delay until I had context that made it clear enough. Plus, readers already have to do a lot of mental work in a first paragraph to get oriented.
I also use “they” in the story to refer to groups, but I think it’s pretty clear when it’s one or the other. Of course, every story is different, so if you are referring to groups frequently in your story, clarifying between those groups and a specific character may take more work.
If you’d like another example, I have another story with singular they that you can read, That Time an Angel Tried to Fix Me.
Beta reading and copy editing are really helpful tools for identifying and clearing up confusing references. If you’re hiring a copy editor, I would ask about their feelings and/or experience with singular they before you choose to hire them. It’s worth noting that a few people just have trouble wrapping their minds around singular they for a named person, even when the context is clear. I don’t try to cater to them when I’m using singular they. Over time, as more people get used to the pronoun, that problem will get better on its own.