In the student biz, and in many professional occupations, a good memory counts. Whether you're trying to recall what happened in 1066, what your client's name is, or even what you're supposed to pick up at the supermarket, a knack for remembering is handy.

Not all of us, however, have perfect memories. This is especially troublesome if you're a student and you are expected to be able to regurgitate historical dates, names and places at the drop of an exam.

Sure, anybody can memorize an individual fact: King John signed the Magna Charta in 1215. But if you pile too many additional facts on top of that, you're likely to push King John right out the bottom of your brain.

Fortunately, rote memory is not the only method. There are tricks. Mnemonics (nee-MON-iks) are mental devices that can help you out at test time and in civilian life, too.

What you do is: Isolate the material to be memorized; then compose a sentence or a jingle (preferably hilarious) that connects the elements of the target material in your mind.

Example: My friend Tom, when in the first grade, had a hard time learning to spell arithmetic." Was it "arithmetic" or "arithmatic"? His teacher told him, "A rat in the house may eat the ice cream." Eureka! Take the initial letters--A Rat In The House May Eat The Ice Cream--and you have arithmetic.

Another friend's teacher taught her students not to spell "separate" with an "e" ("seperate"). She said there is always "a rat" in "separate." This makes no sense in real life, but it helps with spelling.

I was in fourth grade when I learned the nine planets of the solar system and their order, starting with the one closest to the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. How do I keep them straight? Simple. I just rattle off, "My Very Educated Mother Just Served Us Nine Pancakes."

Another faction of fourth-graders learned "Mary's Violet Eyes Make John Sit Up Nights Plenty." This version has the added attraction of forming a complete sentence even before the discovery of Pluto.

In eighth grade, Miss McDermott encouraged the science class to memorize the periods of the Paleozoic Era. The strangeness of the names made this a formidable task: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian and Permian. It so happens that my best friend in the eighth grade had a grandmother named Stella Dorwick, surely an unusual yet unforgettable name.

We immortalized old Stella by ensconcing her in our mnemonic: "Can Old Stella Dorwick Make Prune Pies?"

This tidbit of information about the Paleozoic may seem of dubious value, but for someone like me, taking a geology course nine years later, those periods are still stuck in my mind. I decided to go ahead and memorize the epochs of the Cenozoic Era (Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene and Recent) for this class. I came up with "Playwright Eugene O'Neill Makes Paula Prentiss Recoil."

In French, a small group of verbs uses "to be" instead of the usual "to have" when forming the passe' compose' tense: monter, venir, descendre, etc. Fortunately, their initials form the name "Mrs. R.D. Vandertramp."

Rhymes also work. Who hasn't heard the jingle that warns you away from poison ivy (with its three-leaf clusters) but allows you to pick Virginia creeper, which is similar except for its five-leaf clusters: "Leaflets three, let it be."

And what about the old spelling aid, "I before E except after C or when sounded like A as in neighbor and sleigh"?

There is a well-known jingle for remembering which months have 31 days: "Thirty days hath September, April, June and November. All the rest have 31, excepting February, with 28." This incantation possesses a certain rhythm, but lots of people can't remember it, or they insert "December" where November should go.

An auxiliary mnemonic lies in your knuckles. Place your two index-finger knuckles side by side, and mentally assign a month to each knuckle and to each "valley" between knuckles. Your left pinky knuckle is January, the first valley is February, and so on. The first right-hand knuckle will be August. (You will have one valley and one knuckle left over.) All the knuckle months have 31 days, and all the valley months have 30, except February, which remains the black sheep no matter what.

For remembering a person's name, memory experts suggest you find some characteristic about him or her that suits the name. Remember Miss McDermott? Though I have not seen her for years, I could probably remember her name if I met her on the street and found myself stuck momentarily. You see, she had olive skin, which makes me think of dermatology, which is but a short step from McDermott.

Another method is to create a striking mental image of the person doing something that will remind you of the name. For instance, if Miss McDermott's name had been Miss Martin, I might picture her with really green skin and antennae, like a Martian.

Of course, you will never remember the target material if you can't summon up your mnemonic device. This is why a mnemonic should be simple or humorous or at least memorably offbeat.

If you want to know how many "r's" are in "embarrass," make up something you'll remember. Think of Ronald Reagan embaRRassing himself on a railroad. Don't think, "Ethically meretricious bobbies arraign raucous renegades at sumptuous soire'es," which may be true but hardly memorable.

So--when did King John sign the Magna Charta, anyway?