Mnemonics is the practice of using mental pictures, rhymes, or other devices to aid in memorization.
For instance, the notes on the lines of the treble clef are commonly remembered as "Every Good Boy Does Fine," or E,G,B,D,F, from bottom to top. The spaces are "FACE."
Another method is the "stack." This is especially useful for remembering lists of things, particularly ordered lists. You simply visualize all of these things stacked together in a memorable way. The more outrageous, the better.
I don't know who first came up with this one, but I used it in fifth grade to memorize the first thirteen states, in the order they entered the union. I still remember it. So here it is:
First, you have a DELICATE China Plate. (Delaware) The plate has a crack in it.
A fountain PEN is jammed into the crack. (Pennsylvania) And standing balanced at the top of the pen, is none other than a JERSEY cow. (New Jersey) GEORGE WASHINGTON is riding the cow. (Georgia) He has a big cut across his cheek, and a band-aid CONNECTING THE CUT. (Connecticut) He obviously under a lot of strain, though, because there is an enormous MASS of ice balanced on his head. (Massachusetts) MARILYN MONROE is sitting on top of the ice. (Maryland) Only, for some reason she has a OCEAN LINER in her lap, pointing SOUTH. (South Carolina) In one of the smoke stacks of the boat, there is a HAM jammed inside. (New Hampshire) The ham is wrapped in paper, which is, in fact, the sheet music to "Carry me back to old VIRGINNY." (Virginia) A large building is sitting on the ham, and as your eyes follow it up, up, to the top, it is immediately recognizable as the EMPIRE STATE BUILDING. (New York) The Empire State Building, for some reason, has a weather vane at its tip-top, in the shape of an OCEAN LINER, this one pointing NORTH. (North Carolina) On top of the weathervane ocean liner, perched up there at the very top, pretty as you please, is a RHODE ISLAND RED HEN. (Rhode Island)
It may take a little while to get your mind around all of that, but once you do, there's no getting rid of it.
For more information on Mnemonics, see Memory Matters by Mark E. Brown, or The Memory Book by Harry Lorayne and Jerry Lucas.