When I was working on perfecting my French a decade or so ago, the write/copy method really worked for me.
In French, many people (including me!) find verb conjugation really really hard. There are just so many exceptions and irregular verbs.
I had gotten really good with French. Had long conversations with native speakers, watched films, read novels. Could speak clearly enough people could understand me.
But I was CONSTANTLY messing up verb conjugation.
People assured me it was no big deal. They knew what I meant. But I hated it. I was determined to get it right.
So I went out a bought a comprehensive conjugation workbook.
And for about two weeks, I spent an hour a day copying and recopying verbs with all their conjugations, even the literary ones people don’t use in speech anymore.
I copied until I could do it blindfolded
The mess of French verb conjugation has never bothered me again. The process of copying by hand cemented the knowledge into my brain.
After struggling for years, two weeks of concentrated copying was all I needed.