Sure, I can give an example of learning to memorize playing cards.
I learned a technique to convert a pair of cards into a word or phrase that conjures up a single unique mnemonic image. No big secret here, it was published years ago on this forum. After experimenting with it, I modified the technique to better suit my own brain (and shared an exhaustive explanation and guide to my system as well.)
There are 2652 possible pairs of cards that can be made from a shuffled deck of cards (2704 if you allow duplicate cards.) Each one of those pairs is represented by it’s own mnemonic element.
The structure for “reading” the cards is to look at the suit combination and the two values. These represent unique sounds that are converted to words in order to provide the imagery.
So one pair is read as “jason,” another is “stone,” another is “raven,” and another is “golf.” I had to learn to “read” these cards as if they were words in another language. Through practice (which I’m still working on), I’ve gotten to the point where I can see a pair of cards and “read” the word that it generates in under a second. I’ve basically learned a new vocabulary of 2700 new “words” to represent these elements.
I’m nowhere near as advanced as the top tier memory athletes, but the process is the same. As quickly as you can read the sentence “jason throws a stone” or “a raven plays golf” is how quickly the four pairs of cards can be read. By crafting those elements quickly into scenes like that, they can be stored at locations in my memory palace and easily recalled in the correct sequence.
But the point is that it took months and months of work to get to the point of fluency that I have now, and it will take months or even years more work if I want to get to elite speed with that technique.