I recommend a simple approach.
First, learn about how to properly create a framework focusing on a habit-based approach, i.e. learning what steps to take in a structure question rather than learning or force-fitting existing frameworks onto a case. This can be done by watching some tutorials or videos, however, most effectively with a coach who is an expert for the type of case (candidate-led BCG and Bain style vs. interviewer-led McKinsey style).
I have written some other answers on these points here:
Once you have the methodology down, in the second step, you can practice structure, market sizing, and mental math.
- Structure: Use the case library here and just look at the structure questions, use university case books, create your own structure questions in daily life, and using newspaper articles
- Market sizing: Use the case library here and just look at the market sizing questions, use university case books, create your own market sizing questions in daily life, and using newspaper articles
- Mental math: Use the tool on PrepLounge to create number drills and practice 1 hour a day