The rules are simple. From October 1 to October 31 make four pull requests to an project on Github.
Fix a bug, write some documentation, make some code more efficient or anything else that improves an open source project.
For full details, check out the event page on DigitalOcean. There's a little over a week to get busy, plenty of time to contribute!
If you've contributed to something, make a post on this thread for the Dev Japan Tokyo community to check out!
:jack_o_lantern: :ghost: Happy Hacktoberfest! :ghost: :jack_o_lantern: