The library

Learn each line with the reason for every move, recall it from memory, play it on the clock, then hold on when the opponent leaves the book.

Positions where your games went wrong come back as tests. Solve one clean, and it comes back later to prove it stuck.

Tactics by motif, or puzzles that grow out of the openings you play. The difficulty follows how you do.

The mates and endings that decide games. The method first, step by step, then proving it against a defender who fights back.

One quiet move to find, the alternatives priced, and the continuation that shows why it was the move.

Positions where the move most club players reach for and the move Stockfish wants are two different plans.

Replay the classics with notes where they matter, and stop to find the move before it is shown.

Learn the board well enough to see it with your eyes shut: square colours, knight routes, then whole games without looking.