There are so many Ansible Style Guides so here are the ones that I used to create my own:
More basic ones:
Best practices from Ansible community/Red Hat
Presentation on best practices from Red Hat
More advanced:
Linux Fabrik’s Ansible Development Guidelines
Ansible best practices from Andreas Sommer
Red Hat Communities of Practice role development guidelines
Also certain topics are covered in Best practices presentation from George Shuklin
Bonus – some examples