The New York Times Magazine has a fascinating article by Joshua Foer on memory training. It documents how he went from a reporter looking for a story to a participant to a the new U.S. record holder in speed cards (a memory event in which you memorize the order of a deck of cards as fast as you can).
The method he uses is the art of memory, roughly the method of loci combined with dramatic images. He mentions Dr. Yip Swee Chooi, an interview with whom you can see here. In the interview, you can see how Chooi makes connections between sounds and images.
It's obviously a very powerful technique, both as shown in the video of Dr. Chooi, and as attested in many scientific studies. The question, then, is why do so few language learners employ it? Having tried it myself when learning kanji, I can say I found it very difficult to come up with memorable images. As the article explains, this itself is a skill which requires dedicated practice. Here's where most of us fall down. We're not willing to put in the short term effort for the long-term gain.
Interestingly, Foer mentions that he often fails to employ his own memory talents to daily tasks such as keeping track of his keys or remembering friends' phone numbers. I suppose this is like an Olympic sprinter telling people of course he doesn't run everywhere.