How to build deeper historical knowledge without formal courses

How can someone deepen their historical knowledge without taking formal courses?

Start with a subject you already enjoy, write down the questions it raises, follow them into more focused books, and ask knowledgeable people when you need guidance.

Start with an area of history that already interests you. While reading, write down the questions the book raises instead of treating it as the end of the subject. Use those questions to choose more focused books and build outward from the original topic. When the next reading is unclear, ask someone familiar with the field for guidance and accept that they may need to refer you to another specialist.