To know as much about the life and the interests of the person you are talking to, and to present yourself to them not as a threat but as someone who is interested in what they have to say. The more knowledge you have, the better the interview will go. It's always different with politicians, but with other people, never assume that they don't want to talk. Even people in the most difficult situations might want to talk and tell their story. It's like a continuing post-graduate education.
Every story presents something to learn and to discover.
Most days, I want to learn something and figure out how to present it to other people. But once that dream died when I was about 12, I realized that there was absolutely nothing I was any good at except writing. Figure out who you like and try to study why those writers are effective. Also, rather than studying journalism in school, do it as much as you can. I don't get it very often.