The GEDCOM X project is developed and maintained at Github, allowing us to leverage the powerful collaboration features that Github provides. Github has accumulated a lot of great resources on how to get started at github:help.
If you haven't worked with Git yet, now's the time to start! (We promise, you'll never go back.) Github has accumulated a lot of great resources on how to get started at github:help. Get familiar with the Github M.O., and take particular note of how to fork a repo, how to send a pull request, and how to be social.
To get started with Git, we'd recommend Pro Git.
Well, the first thing you'll want to do is make sure you're watching the project. You might even be interested in following some of the people involved in the project.
The project has a blog to which news, announcements, and other articles are posted.
GEDCOM X is defined by its set of [specification documents|Specifications], which are maintained at Github. The official GEDCOM X repository is established by FamilySearch at FamilySearch/gedcomx. Issues are managed by the issue tracker. Documentation is managed by the wiki.