1. Remember that everything is fallible.This doesn't mean that nothing can be known or that all knowledge is unreliable. It just means that everything has the potential to be incorrect. It is a prompt to think critically, spot inconsistencies, and work to iron out the wrinkles in every story you hear. The truth is that very little of the information we receive is communicated clearly and competently with no error. It would be irresponsible to take it all at face value without vetting it first.
Think about the act of receiving instruction from a veteran craftsman. They will impart their technique and their philosophy to you, but there is still much room for error. They could be using an outdated technique. You could hear them wrong. They could be leaving something out. Or, they could just not be as good at teaching as they are at their craft. All of these possibilities must be acknowledged for you to truly appreciate what you’re learning. Supplement their instruction (and all information-gathering) with independent inquiry.
2. Embrace being wrong.Nobody wants to be wrong, and you shouldn't necessarily want to be either. But if you are wrong, lean into it and let it happen. Learn to appreciate the feeling of letting go of your false preconception. It means that you've just learned something. Being wrong is the first step to being right. Seek opportunities to test your ideas and look for vulnerabilities and weaknesses. It's easy to justify something based on its positive traits, but a truly useful idea must also stand up against adversity.
3. Be domain-independent.Imagine a medical doctor who believes in superstitions - they do exist (the doctors, that is). This is an example of someone who has gone through many years of intense scientific training, yet has somehow failed to apply everything they’ve learned about how the world works to their own belief system. Maybe they thought those two domains are inherently separate. An intellectual, however, is ruthless in their application of critical thought, no matter how personal the subject. While you may specialize in one subject or another, it behooves you to branch out and learn about all others you interact with.
4. Think in concepts, not facts.Facts can be mistaken or misremembered. Concepts are processes that allow you to reconstruct the facts. This is the difference between memorizing multiplication tables and actually knowing how to multiply. One is quick, limited in scope, and easily botched, the other is slow, but more versatile and reliable. Conceptual thinking also allows you to be more creative because you get to decide which parameters to experiment with.
My favorite example of this is a romantic relationship. Most people have hard and fast boundaries for relationships (monogamy, strict fidelity, no sex until the third date, man and woman, etc.) because they’ve been told by their peers and elders that these are necessary for a relationship’s success. However, a conceptual thinker throws all of that out the window and instead works backwards from their relationship goals to imagine their own boundaries. They may end up at the same conclusions, or they may prefer a polyamorous triad with two members of the same sex. The point is that they weren’t burdened by conventional wisdom in developing a plan for themselves, so their range of potential conclusions is more broad.