The way I learned CAD is the same way I approach programming projects. I tackle simple, bite size projects, which then increase in complexity until I have the skills necessary to tackle big complicated projects.

I found that standard CAD to be no simpler than OpenSCAD. Really, the biggest disadvantages that OpenSCAD have is usability and a library which is fixed by using BOLS2.

BOLS2 has the same problem as standard CAD, it is overwhelmingly big. In some cases, I didn't know features were already in BOLS2 so I don't have to reinvent the wheel writing my own inferior library.

So, how to tackle it? Same thing as any learning projects. I just tackle it in bite size chunk.