It’s not race.
One of the biggest things I saw in 2015 was the push to add more diversity to YA books. Many YA authors wrote books where the main characters weren’t white. If the main character was white, the supporting cast tended to be people of color. I’d have trouble naming more than one book I read that didn’t include at least two races.
The idea is fine if that’s what authors want to do, but an author should feel they’re being pushed into changing races or genders just to fit the trend.
Looking back at books, I hadn’t really noticed race much. There were a few older books, like Ender’s Game, that included quite a bit of racial diversity. (The Ender books did a very good job of worldbuilding a future where different races and cultures didn’t fade away.)
Overall, I’d never noticed a lack of racial diversity. It’s pretty easy to forget the race of a character. After all, reading isn’t visual like movies, so skin color is much like hair color. Unless it influences the plot/character or is mentioned a lot, it’s forgettable.
Most books are lacking diversity, but not it’s not racial. What they’re lacking is personality diversity which is much more obvious in the written word than skin tone. Skin color doesn’t make a character unique. What makes them unique are their thoughts and actions.
Authors tend to forget about this sort of diversity. The characters (at least the good guys) often end up having the author’s own moral views. In some cases, not only do the characters not have moral diversity, they don’t even have different goals or personalities.
Characters need to be cut from different materials, not cut from the same cardboard and painted to look different. Without difference of opinion between characters, there is little unique about them.
This is probably why anti-heroes have seen a rise in popularity. It’s because they’re not cut from the same moral fiber as the rest of the cast. In Star Wars, Luke Skywalker and Han Solo had two very different moral outlooks on life, or at least Han liked people to think that. This adds conflict and makes the story interesting, as well as realistic. In real life, not all good people agree. If everyone in a story agrees, there’s very little conflict, and conflict is what drives the plot forward.
Character flaws and misconceptions, often brought on by the life the character has lived, are another good way to add diversity. In Mistborn, Kelsier believed all nobles were evil. This made him act ruthlessly, which wasn’t right, but it set him apart from some of the other characters and added conflict. Because of the world he lived in, the audience could sympathize with him. Characters like this bring up the question, “If I’d gone through what that character did, would I have ended up like them?” If it’s done well, it won’t encourage the reader to act like the flawed character, but it might help the reader learn to show empathy to flawed people in real life.
To add this sort of thing, look around at people and see them as more than a stereotype. Just because someone doesn’t agree with another person on certain issues, or would act differently in a certain situation doesn’t make them evil. (Though, in some cases, it can.) Keep cultures in mind too. Some people might consider horses or dogs to be a food source, while another person would be horrified at the thought of eating them, even if the second person is perfectly okay with eating a cow or pig. Cultural differences can be an interesting source of conflict. Just look at dwarves and elves.
When it comes down to it, it’s best to focus on making unique characters, not just giving them different appearances. A character’s choices are more important than their race or gender.