Ask Slashdot: What Should I Study?

A fellow Slashdot reader is seeking advice on a new field of study: After many years at the same company, I'm now thinking of a change. At my current place of work, I have worked on many different projects, from server side development, to UI development, and most recently, a lot of data science work. If I were to rate myself, I consider myself to be a good developer, thorough, conscientious and always willing to learn new things. Even my recent foray into data science (though not entirely new, since my graduate studies specialized in machine learning) has had reasonable success, and ideally, I'd really like to continue working in this space. But, I'm starting to feel in a rut and I'm looking for a change. And looking outside my company, I'm not sure how to begin. Should I hit the books again? Should I focus on any specific technologies? I haven't particularly kept up with new technology -- after working for so long, I tend to think of that as something I can learn, when I need to. Any advice on how I should go about preparing for interviews? I'm quite willing to put in a few months of work into prep, so all suggestions are welcome!