More related to software, I have another rule: read the official documentation first before going somewhere else. Though often less polished than external books, it comes from the creator and it usually worth the effort.
The official Postgres manual instantly comes to mind whenever I think about great documentation. There's just something about the way it's split up, and especially the typical length of a leaf page, that makes it absurdly helpful.
It's a joy.
When open source was getting rolling in the 90s I don't remember it being nearly so polished.
And at least there's some kind of acknowledged API now (even if the first class languages shift with the slightest breeze).