Let me start that documentation varies based on the type of the project, the kind of documentation, targeted audience. For example, we have two kinds of documentation - internal, which is targeted for developers and is highly technical and external (or public), which is divided into two parts - one is business oriented and the second is a developer oriented. All these documentations have different narrative styles, serve a different purpose and are aimed at different target groups. So, you'll have to keep that in mind.

Now, that this is out of the way, let me share a couple of resources I've gathered through the years:

Writing Docs

writethedocs.org

This is the go-to place for technical writers. It's a community of people who care about documentation. They have Slack channel, learning resources, like a newsletter, podcasts, videos, documentation guide (which you should definitely check), blog posts and much more.

Articles and blog posts

• Teach, don't tell - a post about writing technical documentation. More specifically: it’s about writing documentation for programming languages and libraries.
• Jacob Kaplan-Moss's blog posts about documentation - Jacob Kaplan-Moss is the co-creator of Django and has written a couple of great posts about documentation style, how to and not to write documentation with some general editing tips.
• You are what you document - again, another great post about how to do great technical documentation.

Books

I'm not a big fan of books about documentation. I have tried reading a couple of books about technical writing, which left me disappointed - they were all too narrow and didn't give any advice. Probably I didn't choose the right books back then. That being said, I've heard good reviews about Technical Writing Process and Elements of Technical Writing, so you should definitely check them out.

Stripe has some good content on documentation on its digital magazine Increment. increment.com/documentation