Any useful rule is fine as long as it's understood by everyone in the team.
Use your best judgement and make exceptions when needed.
Code style
Way of working
Testing
Error handling
Versioning and releases
README template
Project boilerplate
Package development
Best practices
File structure and naming
Styling and CSS
Miscellaneous
Gem development
Rubocop
Tips & tricks
Services
Using GitHub Actions best practices
Writing GitHub Actions best practices
GitHub Actions issues and limitations
Social media
Design resources
Good Enough™ regexes