How and what to learn
The only skill you need to learn
“Give a man a fish and you feed him for a day. Teach him how to fish and you feed him for a lifetime.” — Lao Tzu
Information is abundant, so are teachers especially in video and book forms. Searching will provide all the answers, the challenge is filtering them.
There are no silver bullets
Here are the usual filters, and their problems:
Choose science and math: numerology may look like science.
Choose the most reputable sources: new sources may have no track for reputation, old sources may be outdated. Appeal to authority fallacy.
Choose experience: confirmation bias, superstition (overfitting to the irrelevant).
Choose truth with predictive value: self-fulfilled prophecies, confirmation bias.1
They all may be useful, especially when combined, but be aware that even all of them combined may fail.
How to learn
Be skeptical. Keep a healthy dose of doubt, and ask yourself if alternative explanations are possible. Keep an open mind, but be unwavering in your attempts to discard what is not true. Find principled ways to discard both assumptions and possibilities.
Study and practice. If something is not applicable, do not study it. Practice will give you reality checks. Study should help you to escape local maxima and self-reinforcing practices. What is not applicable is idle speculation, do not engage in it.
Generalize. Develop a personal taste for what seems to be coherent with everything else and what may be useful, if not in the current context, in other potential contexts. Personal heuristic: what is useful is more important than what is true. What is useful in one area is likely to be useful in a different area, either being a basic principle, or an example of a deeper principle. “Reality” is universal, not local.
What to learn
Anything is better than nothing. Start with the sciences. After you have the previously mentioned personal taste, follow your curiosity, and learn to make better questions. Personal preference: asking for the purpose of something. A purpose serves as a compass.
There was a time when people thought that a mathematical theory of communication was not possible. In an earlier time, quantifying temperature was a laughable idea. Solutions become tools for other solutions.
Do not assume knowledge, objectivity, or certainty are impossible.2 Even when they are (see Gödel's theorems) do not assume that eliminates the possibility of empirically useful solutions. Universal solutions may be impossible for some problems, but partial solutions may be good enough for your purposes.
Every person has pain avoidance as a purpose at some point in their lives. Actions may focus on several areas, the main ones are two: stop feeling the pain, or stop the existence of the pain cause. The latter requires more effort, but it is usually more effective for improving the lives of other people. The only reason to prioritize one over another is opportunity cost. BTW: opportunity cost is something useful to learn about.
PS: This entry was motivated by a question I received on Reddit, asking if Reddit helped me to know more about marketing.3 I do not remember asking anything, but I know nothing about marketing, so I guess the answer is "no". I decided to upgrade the answer to how and what to learn (in general) because I think this is more useful. As a reminder, please feel free to ask anything, and if this serves as an example, I will probably answer something else.
About Reddit, it is a place like any other. You may find useful information. You will find plenty of useless and harmful information. If you know how to filter it, you may try to use it for its information, but you are more likely to find other sources more efficient in your efforts. Reddit may be the best place to find information about the Reddit community, i.e. its users, if that is relevant to you.
About marketing, the first thing to ask for is the purpose; what problem are we trying to solve with marketing. There are a number of problems within the area, each one may be solved with a different set of tools, methods, principles, and approaches. Some are better avoided than solved. But I know nothing about marketing.
Confirmation bias is twice in the list because it deserves to be. Avoid the delusion of knowledge.