Creating your Avatar using UniVRM
There are two common methods to create a VRM, UniVRM and the 'VRM for Blender' add-on. As noted in the VRM Creation doc, there are multiple ways to create your avatar, rig, and then create the VRM itself.
Generally speaking, UniVRM is an easier approach that also allows you to test the spring bones (if you decide to add them) in Unity directly. It also seems easier to add materials using UniVRM. The only catch is you have to use it within Unity.
The following tutorials assume that you already have an optimised character ready to rig and create the VRM with.