>>14037482Read the book 'Make it Stick'.
The basics:
Retrieval practice - you should test yourself about the things you want to learn.
Spaced repetition - you should delay your self-quizzing to allow some forgetting and therefore strengthen your knowledge.
Interleaving - mix up the order of your study, avoid practicing the same thing for too long. Massed practice FEELS more productive because you're using your short-term memory, but at the long run these benefits vanish.
Important note: struggling is part of the process, in fact, the book states that it is good because it changes the brain. It also states that the extent of our mental capabilities lie mostly within our control.