The main idea from lesswrong is to prefer textbooks over other other books.
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.
And the fact that you can usually find the exact page you want from Google is nice. As a bonus, if google gives you the wrong version, that page links to the same page for every other version too.
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.