Well, the immediate answer is to support comics that are worked on by women and minorities. If you happen to like Superior Spider-Man, there's no reason you should stop buying it just because the creators on the book are all white men. But if a book comes out that might suit your fancy and happens to be created by people who aren't white, heterosexual, cisgendered men, you should absolutely take a look at it.
"But, Sean," you say, "that almost never happens at Marvel or DC!"
Right! Which is why you need to look elsewhere. Here's a shot of what I picked up at CAKE a couple weeks back...
"But, Sean," you say, "I don't live in an area that has conventions that feature a diverse group of comic creators from whom I could purchase their independent comics, thereby supporting them."
The latest three Kickstarter projects I backed are: Capitalism and Other Stories, My So-Called Secret Identity and Unsounded. All of which are heavily, if not entirely, worked on by women. All of these are (to me) great-sounding projects, regardless of the genders or gender identities of the creators involved. I'm willing and able to put some of my money towards these projects.
But, frankly, I think there are lot more interesting projects going on here than at Marvel or DC.
So if you want to do something to help mitigate the various -isms in comics, use your money to support projects and creators you believe in. I don't buy anything JUST because it was created by someone who fits a certain demographic, but I do try to keep my eye out for projects that fall outside the white, heterosexual, cisgendered "norm" and will lend my support to those creators who do good work. Because that support encourages them to do more, presumably of at least the same caliber. And more good work by women and minorities is absolutely what this industry needs.