Learn, understand, challenge, repeat.

Learn as much as you can about all sorts of topics, even if you don’t have specific plans for those topics

Learn enough that you don’t just know the facts, but that you actually understand why things are the way they are. You should be able to predict things you haven’t yet learned if you understand the concepts. If you don’t understand something yet, keep learning.

Learn your fundamentals: language skills, math, logic, statistics, the science of research, history, politics, basic psychology, and the physics of whatever realm you’re operating in (meaning that in today’s day and age, you should learn about both real-world physics and about how information flows on the Internet).

A lot of people don’t know how to teach themselves, so it’s probably important to point out that learning to do so effectively is a big part of thinking for yourself. Learning how information is presented, as well as what’s often left unsaid, is important. Learn how to read graphs and charts and statistics. Improve your information literacy: Learn how to find credible sources, how to judge the credibility of a source, and what “credible” actually means. It doesn’t mean infallible.

As a general rule, don’t accept a fact until you have multiple credible confirmations of it. That might not be possible, but when information comes from untrustworthy sources, remember that. Learn the difference between something that you’ve learned and accepted and something that you’ve just heard on social media a few dozen times. This is easier when you have an understanding of what you’re learning. True things fit in better with other true things.

Don’t assume things are false just because the source isn’t credible, either. Just do extra research to verify. Do your own experiments to confirm, if possible.

Sometimes you’ll realize something you’ve accepted might be wrong, possibly because it conflicts with something else that you learned. When facts don’t add up, challenge them. You’re not infallible. Replacing a fact you accepted long ago isn’t a failure; it’s a victory. Many people are incapable of doing so.

Learn to distinguish between facts, inferences, theories, and opinions. (Note that established, accepted scientific theories often fall into the “fact” category.) Facts are verifiable. Inferences are based on facts; they’re evidence-based conclusions that can help to build theories. Theories are explanations, and they can be disproven but haven’t been proven (else they would be facts). Information presented as facts can be false. Theories and inferences can be poorly formed, even if the facts are sound (and especially when they are not). “Opinion” is a word people use to defend flawed theories. If the opinion isn’t a preference, there’s a good chance it isn’t an opinion at all and is just intentional misinformation. “You can’t argue with my opinion” isn’t applicable when the “opinion” is provably false - then it’s just a failed fact, inference, or theory. And even when it is an opinion, it can still be criticized.

Learn about logical fallacies. Even if you don’t call out the person using them, try to notice them in the wild, both by people you agree with and people you disagree with. But especially by people you agree with. Learn how to notice other ways people are misled.