I wish I could tell people how to get into people analytics. They're often coming from an HR background but have a strong interest in the data side of their work, though others have an analytics/stats background of some kind and aren't sure how to move into people analytics specifically. There are just too many examples of how people arrived at their first people analytics role — it's different for everybody.
But what I can do is share a bit more about my own journey. I have no idea what benefit it will be, since everybody's is unique. I'm leaving out a number of details to keep it brief.
I started undergrad as a math major before I took an economics class. I eventually became interested in behavioral economics, and considered doing a Ph.D. before I realized I liked reading economics research more than writing it. A mentor suggested that working in HR would be a good opportunity to combine my interest in "why people make the decisions they make" with practical opportunities for impact. Since my degree wasn't getting me any HR job or internship opportunities, I went for a graduate degree in HR.
My grad program was quite flexible and I was able to spend a lot of time learning more analytics skills. It was there that I learned R (thanks to Gabe Gershenfeld, who I briefly interned for), took a machine learning class, and pitched a professor to teach me and some others two semesters of courses where we were basically learning R and applying it to whatever HR-ish data we could find. Andy Lowrey and I entered people analytics case competitions, I got on the phone with people from LinkedIn who appeared to be doing people analytics, and I read everything I could find on the subject on Twitter and LinkedIn.
After deciding not to return to the company I interned with, I was on the job hunt. It was discouraging that nearly all my classmates had landed jobs, and I was still looking, when the CEO of a startup in the people analytics space reached out to me on LinkedIn. I ended up taking a job on their sales team, which allowed me to go to a number of conferences and have more conversations with people analytics leaders.
Eventually a connection approached me about an open people analytics role on their HR team, where I went for my first internal people analytics gig. Later I moved on to Facebook's team, where I am now.
I wouldn't expect anybody else to take the same path I did, which is why I don't share my journey very often — but for whatever it's worth, here it is.
I also recommend Jared Valdron's article on starting a career in people analytics: https://www.linkedin.com/pulse/qa-starting-career-people-analytics-jared-valdron/