I have been studying C4D for about two years. Before that, I only made MAYA character animation, but I don't have any knowledge of rigging. I downloaded a lot of C4D projects online to learn XPRESSO knowledge. Reverse learning is my only learning. Way, I searched for tutorials related to rigging in youtube and vimeo. When I have a certain rigging foundation and I am familiar enough with C4D nodes, I started to learn Maya's rigging knowledge. I converted him to C4D. It is completely feasible.
At the same time, I like math and programming, so I will learn some 3D mathematics to understand the mathematical principles behind rigging, which is very useful for me.
If you want to advance, this is the way to go!