Perhaps writing, but not sure how to make it minimal and fit into daily routine. Maybe something like Japanese Sentence a Day Challenge
Getting corrections in LangCorrect.com could give some better understanding of grammar. What you were led to believe to be, but not really so.
imo, it’s still a different skill from s proper two-way communication, but I am not quite a conversationalist myself. It may help to get a private teacher, or make a live chat for that. There are also several Discord for the purpose.