This page is still a work in progress.
Check out these existing resources for contributors:
Beginners Guide to Contributing.
The complete guide to hosting and publishing plugins
The plugin tutorial will get you started with Jenkins plugin development
Adopt a plugin
Advice before creating a new plugin
How we handle pull requests to plugin repositories
Check out the jenkinsci organization on GitHub for plugins and other components to contribute to.
Jira query for issues we believe are beginner-friendly