Read: things you disagree with; spy-stuff -- like soviet defectors to the West; detective novels; about applications of game-theory -- like how to win at poker.
There are a few ways to get you going:
- The "5 whys"
- "First Principals thinking" (popularized by Musk),
- Challenge and validate assumptions
Read as much propaganda as you can. The more opinionated, the better, but be sure to not miss one side.