The Guide is the main "how do I learn Japanese" primer made by members of the Daily Japanese Thread. There are several other primers describing how to learn Japanese on the internet, but this is one of the most visible, and the one I'm closest to.
The Guide was collaboratively written by several pseudo-anonymous contributors and is public domain. It's split into an introduction, a few background explanations, a list of the aspects of the language one needs to study, instructions on how to approach them, a list of resources, and an FAQ.
As of writing, this is the current "official" version of The Guide: https://djtguide.neocities.org/guide.html