Start with reading that makes economic reasoning concrete. Useful -listed books include The Undercover Economist by Tim Harford, Poor Economics by Abhijit V. Banerjee and Esther Duflo, Doughnut Economics by Kate Raworth, Fifty Things That Made the Modern Economy by Tim Harford.
Use the books as starting points for questions rather than as a reading trophy-list: after each chapter, write down the model, assumption or piece of evidence that changed your view.
For video study, use CrashCourse, EconplusDal, Institute of Economic Affairs to consolidate diagrams, policy debate and core vocabulary before attempting harder problems.
Treat introductory video as scaffolding. Once the diagram or vocabulary is secure, test whether you can explain the same idea with a numerical example, a graph and a policy implication.
For audio, Freakonomics Radio, The Indicator from Planet Money, More or Less are useful because they train you to interrogate data, incentives and public claims while listening for assumptions.
After listening, practise separating the economic claim from the evidence used to support it; that habit is directly useful for interview discussion and personal statement reflection.
For more structured work, MIT OpenCourseWare: Principles of Microeconomics, Marginal Revolution University: Principles of Economics, Microeconomics, and Khan Academy: AP/College Microeconomics can help ambitious applicants move from school-level concepts towards university-style problem sets, lectures and diagrammatic fluency.
Use Khan Academy mainly for drilling fundamentals, then move to MIT OCW or MRU for harder applications and problem-set style practice. Keep a short reading log with three columns: claim, evidence and objection; that format is useful preparation for both personal statement drafting and interview discussion.