If you want to live fun and free with data viz, it's important to nail the fundamentals. This site promotes the foundational principles all stunning visuals are built upon.
The trick to learning is to break the pursuit down into simple steps. Then start skipping the long path ahead. Don’t walk or run. No, I recommend skipping because it’s much more fun.
My favorite place to learn data visualization and design is the International Design Foundation. They strive to be the Ivy League of online learning for these topics and I believe they have done it. Their programs have not only changed the way I think about my profession, but also given me the confidence I need to back up my design decisions in front of senior stakeholders.