How to Practice Memory Sports

I've always been curious because there's not much documentation on the early years of memory sports. There's like some documentaries, but it's always nice to hear of how it was sort of. Let's get into some, some, into memory sports and some of the techniques that you use. So just to start off what card and number systems do you use. And did you use different systems before and transition to the ones you use now? I am currently using a four digit number system, and I am using a two card system.