I can’t say my inbox is overflowing with people asking me how to learn data visualization, but it does happen from time to time. And when I do get the chance I am happy to recommend the Interaction Design Foundation. They won’t be for everyone, but keep reading to find out how I have benefited and what you might gain from their courses.
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.