Miss Piggy as oracle; Miss Piggy's Guide to Life, as told to Henry Beard. New York: Muppet Press/Alfred A. Knopf. $12.95.

Miss Piggy, the femme fatalem who took the insult out of the word "pig," has at last agreed to share the secrets of her charm with eager readers. "Eager" is the operative word -- enough of them have shelled out $12.95 to put this basically one-idea book on the bestseller list. Some, of course, are more eager to discover why a muppet ranks high personality-wise than to model themselves on the author.

In any case she offers some useful self-help tips:

To divert "unnerving attention" from your new hairdo try putting a bit of spinnach on your front tooth.

On the other hand, "never color your teeth" or powder your tongue.

If you must diet, remember that "the hefty artichoke" weighs more than "the light-as-a-feather pastry," and never "eat anything at one sitting that you can't lift." Don't be discouraged if this diet doesn't work, since inflation applies to dress sizes as well as prices.

"The essence of managing money is managing to have enough of it. . . ."

If you enjoy sauce but not snails, order escargots and "tell them to hold the snails."

When it comes to cooking, don't neglect the "handiest appliance in the kitchen," the telephone. Use it to place your order, then, "when the doorbell rings, dinner is ready."

And "when you are in love with someone," writes this true successor to the girl who doesn't live next door, "you want to be near him all the time, except when you are out buying things an d charging them to him."