gradual acceleration

Czerny's systematic approach of beginning every new étude at a slow tempo and increasing the metronome marking by small increments over days or weeks until the target tempo is achieved.

Czerny was explicit in his method books: no étude should be played faster than the student can play it perfectly. Set the metronome 10% below comfortable tempo and master that, then increase by 2–4 BPM. This is slow work, but it is the only reliable path to clean velocity. Jumping to target tempo before the fingers are ready creates habits of tension that are very hard to undo.