How can I become smarter?

What is “smart?” Howard Gardner at Harvard posits seven different kinds of “smarts” including movement, artistic, etc in addition to math and science kinds. Here's one summary:  https://www.verywellmind.com/gardners-theory-of-multiple-intelligences-2795161 

If you want to become more aware of how the world works, READ READ READ. We have 11 family principles. #7 is “Read or you will have nothing to say.” Read widely—science, cosmology, evolution, climate change, culture change, politics.

THEN be careful never to assert your opinions as if they were facts. Avoid the stative verbs, to be. Never assume you are automatically “right.” Listen. Try to understand other people’s AND your own VABEs. When someone says “This is the truth.” be wary. Usually it’s in reality an opinion. Here's one summary of Albert Ellis's concept:  https://en.wikipedia.org/wiki/E-Prime  

Don’t be too quick to share what you’ve learned. Beware of the Dunning-Kruger effect (Dunning–Kruger effect - Wikipedia ) in which people who know a little overestimate their understanding—they know just enough to not know what they don’t know. People tend to overestimate themselves—everyone wants to be “above average.”

If you love to learn, and you read read read to satisfy your curiosity you will come to understand more about the way the world is. Don’t worry about what others say about whether you are smart or not. Smart is as smart does.

I relied on what others told me for a long time. Eventually I realized that much of that was rubbish. When I retired, I wrote a book, A Song of Humanity to provide a evidence based alternative to all of that. Check out the Table of Contents.

Learning is a life-long pursuit. The day you stop learning is the day that will be just like yesterday.