I know you said that you aren't looking for something like Anki, but: if you want to improve your general memory, there is really no better method than spaced repetition. It doesn't need to be Anki or even a software program; the Leitner system, for example, just uses basic flash cards.

https://en.wikipedia.org/wiki/Leitner_system

I liken a spaced repetition system to any other tool that helps you improve basic functions. For example, while you could brush your teeth using your finger, it's infinitely more efficient with a toothbrush and even better with an electric toothbrush. It's just a tool to accomplish a particular physical task (in your case, improving your memory), so why not pick the best tool?

Otherwise, I've read a lot about the benefits of blueberries. And you really can't go wrong with sleep.