A book by Harry Lorayne (1989) that gives step-by-step
instructions for several memory improvement techniques, for specific areas such as lists, sequenced lists, numbers, faces, names, and cards.
In this book, Mr. Lorayne explains the importance of observation, training, and practice in improving one's memory. He starts with a basic linguistic system based on relating consonant sounds to numbers, learning key systems (the "peg" system, the "link" system), and teaches how to apply these to the memorization of long lists or numbers, phone numbers, etc. Then the book progresses to special topics such as names, faces, and playing cards.
I was skeptical when I saw the book, but bought it anyway. I have been pleasantly surprised at how well the systems work. I can't say that I have developed a photographic memory, and I can see that what you get out of the book is proportional to what you put in. I'm in a job and lifestyle that don't require much memorization, so I don't practice this all that much. But when I've tried the techniques mentioned in the book, they work.
Should you have a reason to memorize a lot of things, and find yourself relying on rhymes, songs, or other tricks, read this book or one like it...it formalizes and improves upon these well-known concepts.