Ask HN: Open data as a career – what to learn?

I've been increasingly interested in pursuing a career (or at least doing some work) at open data, by which I mean ie. opening and managing government data and APIs.

I think that one should be adept at least in different API techniques and database systems, but what else would be good additions to an open data expert's toolbox? Data visualization and other ways of making it not only accessible - but understandable - would also be of value?