I have a thread where I talk about preparing for and taking various levels of the writing exam Kanken.
There are a lot of resources dedicated to that exam specifically.
Nowadays, I mostly just practice writing when I have some extra time in the day. I’ll often ask my wife to give me random words to write and see if I can remember how.
I’d like to give Kanken another go at some point, but the next level for me (pre-1) would require an insane amount of prep.