Answer:
Concisely, "most" memory techniques convert verbal information into visual information. The reason this works is our visual memory is stored in long-term memory faster, it's easier to retrieve from our memory and it lasts much much longer. [Sometimes a lifetime.]
This conversion from verbal to visual does require some creativity though, which can even take longer than just using rote memorization, which is why most people revert back to using rote memorization even when they know to how to create a mnemonic visual image.
Other "verbal" memory techniques are acronyms, rhymes, and songs but these can all require creative time too.
IMHO it would be benefical to students if instructors took the time to create mnemonic devices for their students. Then a student could decide if they wanted to use them or not. As an example I'm certain a second grade student didn't create the "In 1492 Columbus sailed the ocean blue". And yet that little rhyme is how most people remember the date. Of course some mnemonic devices could get an instructor fired if they shared them with their class.