This is one of my favorite ways of helping, because it involves more reading, which is great! It also operates on multiple levels. It is also surprisingly controversial.
Perhaps the controversy isn't that surprising. I had read one article where K. T. Bradford read no white, straight, cis male authors for one year. I thought it was a good article and made good points, but there were many articles taking offense. I won't link to those, but here is the original:
In the offended response I read most recently, I noticed two complaints that made it hard to take him seriously. He acted like she had said to never read a white male author again, when "for one year" is even specified in the title, and he asked why she didn't recommend diverse authors instead of just condemning the straight white males. She made several recommendations.
The other thing that I think is worth pointing out is that it appears that her primary genre is speculative fiction (because sometimes there just isn't enough science to call it science fiction). You would think that in a genre where anything can happen there should be a lot of variety, but there are some common prevailing attitudes written by a lot of authors with the same viewpoints. Seeking out different authors makes a lot of sense for that, and it reinvigorated her. That is a great result.
It doesn't necessarily have to go that way. You might see that you already read a lot of male and female authors, but they are all white, and so make an effort to alternate with authors of color. Honestly, when I started thinking of this I wasn't initially thinking about adults.
I was thinking primarily of children's books. It has been common knowledge for books and movies that girls will accept male protagonists but boys will not accept female protagonists. That makes it safer to make male protagonists, except that also reinforces that boys have no reason to be interested in the personalities or problems of girls. Is it possible that might have something to do with adult men not seeing why women should get equal pay or be able to refuse unwanted attention?
If reading becomes a way of building empathy (and it is), then it becomes very important to fill the formative years with lots of different kinds of people. Books are a way of making others accessible. White boys are already very well represented. I'm not saying that's a reason to exclude books about white boys, but if you did there would probably be enough representation through television, movies, and personal experience that no children are going to forget that white boys and men are people.
If there are no books about black boys and girls, and other races, and handicapped children, and other religions, it seems to send a subliminal message that they aren't fully realized. There is the norm, and they fall outside that so are just a little bite less.
We talk sometimes about representation and being able to see someone like yourself, and that's important, but being able to see people unlike yourself is huge.
I wrote recently about comics, and how men writing women often get it wrong. That's not saying that men can never write women, but there should be women writing. There should be writers of color. Publishing should be recruiting writers out of all walks of life.
They need to be doing that because breaking into publishing is hard. Most of the people who have the kinds of contacts that can help them out will be more of the same. But each new face that you bring in can have a cumulative effect, breaking down barriers.
They will then write more interesting and enjoyable things than before, because the variety of viewpoints will keep things from getting stale. They can open up new markets which seems like it should be tempting. There is often this idea that "oh that won't sell", but there are often hard numbers that prove the naysayers wrong.
I wrote recently about looking for black female musicians, and finding far more than I had dreamed of; it is like that with authors too. Even though there need to be more diverse writers, there are some out there now. If their books start getting more attention, it can pave the way for others to join their ranks.
In the meanwhile, you will have learned so much more about the world, and will be seeing a constantly bigger picture. There is lots of help already out there. The links below are just a starting point.