Rubber Duck Debugging: explain your code line by line to an inanimate object.

Use a pointer or your finger to guide your eyes. This can increase reading speed by 25%.

Follow the 20-20-20 rule: every 20 minutes, look at something 20 feet away for 20 seconds.

Write documentation as if the next person reading it is a violent psychopath who knows where you live.

Use the Feynman Technique: teach what you learn to someone else to identify knowledge gaps.

Take brief notes after each chapter. Summarizing helps cement knowledge.