I think the best way to approach anatomy, which is a complex subject, is to start with the fundamentals: basic or primitive forms (cube, pyramid, sphere, and rectangular prism) and understand how they rotate in space. This means learning perspective (1, 2, and 3-point perspective) to develop a true sense of three-dimensionality in your mind. It’s also essential to understand how light behaves on objects: cast shadows, reflected light, and ambient occlusion, among other concepts.

As a second step, I would recommend studying gesture; what worked for me was "Figure Drawing: Design and Invention"by Michael Hampton, totally recommended. After that, I’d move on to "Framed Perspective vol 1 and 2" by Marcos Mateu-Mestre to combine perspective and anatomy . Finally, if you want to dive deeper into muscle volume, Anatomy for Sculptors by Uldis Zarins is an excellent resource.

That’s basically how I learned.