Many believe that tackling super difficult problems is the best way to improve math skills, but this might not be the case. Research shows that beginners learn best through direct instruction, not open-ended challenges. The key to progress is acquiring foundational skills through deliberate practice, whereby one works just beyond their current abilities making small adjustments. This form of training, supported by extensive research in talent development, is superior to all others. Worked examples and scaffolding are critical for success when mathematics becomes challenging. To enhance understanding, focus on deepening existing skills before tackling advanced ones. Ultimately, deliberate practice is the key to excelling in any domain.
https://matheducators.stackexchange.com/questions/27964/how-to-choose-a-textbook-that-is-pedagogically-optimal-for-oneself