When I started learning, I found that the best way for me to remember was to build my own table of verb stuff and add to it as I learned so that I could look things up that I should know. The good news is that Japanese verbs etc, are simple enough that you can fit all of the info you need on a small piece of paper.
This is an early version of it (Sept 2020, apparently 
) for godan verbs (may contain errors, do not trust):
So for a trivial example, if I wanted to say ‘want to swim’, I can see that the ‘want’ part means adding ‘たい’ to the end of the い stem of the verb. So starting with 泳ぐ, you get the い stem which is 泳ぎ and add たい, 泳ぎたい. Simple. I had a second table for the て / た forms of the various verb endings, and another for the ordering of more complex things, so I could say 泳ぎたくなかった or whatever.
Anyway, this is a long winded way of saying keeping track of what I learned in some handy format so that I could go back to it if I needed to refresh my memory was much more useful to me than verb drills or textbook exercises. In the end, once you’ve learned it and put it in your learned things list the only way to embed it in your brain is to use the knowledge over and over again.