Reason from first principles. The simplest solution is often the best one. You should evaluate ideas from a microeconomic perspective. Use supply and demand. The trick is to find something that is in high demand, with low supply. You can also improve upon existing supply to meet the needs of demand. This doesn't have to relate to business. It can help with personal matters as well. Think about finding a partner. People want to find someone who is in high demand with low supply, ie. not average. This is why the most conventionally attractive people are those who have great faces, bodies, etc. If everyone were super fit and physically attractive, people would look for other characteristics. The supply would meet or exceed the demand. Side note: This may become a reality with upcoming genetic modification technologies where people can choose how their children will look, what genetics they will have, etc.
Knowing the foundations well is better than knowing the complex things a little bit. Learn skills and grasp ideas that are fundamental to the topic you are focusing on. Microeconomics? Grasp supply and demand, perfect competition, monopolies, etc. Want to write better? Learn persuasion, learn psychology, learn how humans think. It's more helpful to learn those things than to learn complex verbiage or how to construct paragraphs and sentences.
Think about your own life from this perspective. Look at where you are and where you want to be. If you are not where you want to be, you have a problem to solve. That problem can be solved by reasoning from first principles. Not fit? Look at your diet, how much you exercise, etc. You aren't fit because of some unique characteristic that only affects you. Think back to the bell curve. 99% of successful businesses share similar traits and 99% of fit people share similar traits. There are outliers, but they should be ignored. What worked for an outlier will not work for you. Focus on the commonalities in those who are successful at what you want to achieve. Then, reason from first principles and get good at the basics of that.
But make sure you are spending most of your time engaging in practice, rather than studying theory. Learn the basic principles and how they work, then practice them. You don't need to know everything to start. Far too many people are susceptible to overthinking. They never feel as though they are ready. In the end, they never end up starting. The beauty of it is first principles can be grasped quickly because they are the foundational level of a topic.
What you want to focus on is systems with short feedback loops. A startup is an example. A startup will publish a new update and immediately garner feedback and make changes. They spend small amounts of time creating without user feedback and most of the time creating with user feedback. This puts them ahead of big organizations planning long-term projects with uncertain knowledge of customer demand.
Focus on the first principles. They show up everywhere, are easy to grasp, and have short feedback loops since they appear in the majority of cases.