While working on another piece, I ran across this post: Seven Things I Learned About Data Visualizations. It's a short list, with details, of how this particular subject taught the writer a few things. It looks at a variety of other pieces, in different subjects, and interprets these items with relation to data visualizations. In addition to being an interesting read, it's a great career piece for the author.
If I were looking for someone that could help me produce data visualizations, this piece would mean much more to me than a dozen questions in an interview. I would have a much better understanding of how this author looks at the subject, and I'd have a frame of reference and some topics to discuss in person.
This article allows me to complete quite a bit of due diligence for someone before I would even meet them.
This is a great example of how you could produce some work on a blog that showcases your knowledge, but more importantly, showcases your thoughts. This is the type of work that gives an employer confidence that you understand a particular subject.
This gives you a brand in this subject area.