Or so says Claire Light:

…how do you — not “become a good editor” but — change the way you do business so that your editing becomes more than an exercise in futility? Here are some steps:

1. Go out an read diverse stuff. This is not hard. There is google. Go to google and look up “African American fiction anthology,” “Asian American fiction anthology,” “New Women Writers,” “LGBT Fiction” etc. Check these books out of the library. Read them. Then pick the two or three writers whose stories you liked the most AND WHOSE STORIES YOU HATED THE MOST, and read a book each by them. Look them up on wikipedia and find out who their influences and mentors were and read a book each by them. Etc.
2. Go to Wiscon, Diversicon, Gaylaxicon, whatever, and talk to people who don’t look or talk like you. Ask them what they’re reading and what they think you should be reading (the answer to these two questions will usually be different.) Take notes. Then GO READ some of what they told you to read.
3. Send your calls for submissions out to all the people of color you know and ask them to forward it. Follow up with them a week later and ask them where they sent/posted it. Sign up for those lists/groups and follow up on those lists/groups a week later with a personal invitation from the editor to EVERYONE ON THE LIST to submit work. Also go here and send calls for subs to these folks and follow up. ALWAYS FOLLOW UP!
4. If you are a real editor, then you live in a real city with real readings. Go to them. Ask around for the POC/LGBT/Women’s/whatever readings and attend them. They will be mostly boring or painful. That’s how it is. You have to dig for gold. Keep going. Every time you go, talk to two people you don’t know, especially if they look like they’re in charge or if they know a lot of people. Ask them to recommend other readings in the city you should see. Carry cards and call for subs fliers with you. EVERY SINGLE TIME you see writer you think is remotely good, hand them a flier. In fact, hand them to writers you don’t think are that good either, and ask them to pass it around. Do this in every city you go to.
5. Keep doing this. This is not a remedial course that will eventually finish, after which, you will now be diversified. This now how you do your job. Keep doing your job.

If anyone was looking for a primer on this subject, they would do well to read the whole post.