If you want to practice hard pen calligraphy, do any experts suggest how to teach yourself? Whose copybook should I learn?

It doesn't matter who you learn from, as long as you like it and feel good. You know what a copybook is, first trace a few lines to find the feeling, then copy it, that is, write it on another piece of paper one by one, gradually stop reading it, and then apply it to your usual writing. That's how I practice. It's quite effective and the handwriting is much better. Start (a disease)