What makes a man smart?
I am not smart. I will tell you what I do.
Read. When I was young, my father showed me the back of the Atari cartridge while he was on the phone and said "If you just read those directions, they will tell you what to do."
I have read voraciously ever since.
Listen and Think. David Mamet wrote in Heist "I tried to imagine a fella smarter than myself. Then I tried to think, "what would he do?""
Stop and Think. Here's a secret. You rarely make decisions based of thought. You often make decisions based off emotions and rationalize them later.
Avoid Dogma. Dogma is literally the opposite of thinking. It is avoiding thought, and becoming subservient to the will of another person, religion, or organization.There are many heinous consequences of dogma, and the desire to lose yourself to it is quite strong.
When you "pick a side", then you cease to be concerned with the facts, and only become concerned about winning. Science is not something to follow, it is simply a series of steps performed that allow us to prove that something happens. That is useful.
Be Skeptical. Primary education is about enforcing the Status Quo. Schools are interested in producing a taxpayer base that can read, write, do basic math, and follow directions. Do more than that.
Question Everything. Most importantly, what you already think you know. Does your source have an agenda? If they aren't independent, don't believe (i.e. think without proof) anything they say. Are you living in a filter bubble?