Is a planning-centric approach a taboo? Maybe, if it's just another word for railroading. Personally, I plan a lot, but I never plan how the story will unfold. Instead, I focus on two things: 1) NPCs and their motivations (why they do what they do), so it's easier to improvise their responses to the players' actions, and 2) places that are likely to play a significant role in the game and what is happening there when no one is looking.