April Fool's Day once again, and yet how rarely is it truly kept.

One of this newspaper's counselors (we have a lot, on the theory that people love advice for other people) said just yesterday that we should not drop 18-inch plastic snakes down the bosom of an 80-year-old lady; nor should we (she went on) give a fellow an exploding cigar since he is almost sure to be drinking wine at the moment of truth and it's expensive to clean the rug.

Piffle-paffle. Mere tilly-vally. Who among us has ever even thought of dropping an 18-inch plastic snake down a dowager's bodice? What we really need are guidelines and illustrations, not silly warnings.

You will examine the following examples to see whether they are good pranks, good ploys, for April Fool's, and I shall briefly analyze them later. Example A

You receive in the mail a notice:

"Do not, repeat NOT, mail in your Census form. The government has determined that instead of these forms, which are susceptible to fraud and outright lies, all citizens will instead appear in person.

"Six convenient regional centers will receive all citizens. You and your family will report to Center No. 3 at French Faddle, Ga., on May 17. All travel expenses will be paid by the government (maximum of $21.87 per citizen) and remember three new provisions of this Census which might be overlooked, so remember:

"Serial numbers of any bicycles you possess.

"Photostats of any tattoos your great-uncles may have worn. This provision does not apply to great-aunts.

"Affidavit (certified) of gross adjusted weight for all zinc or zinc-plated vessels in your possession.

Washtubs larger than 47 by 19 centimeters are exempt from this requirement."

This is, in fact, the text of a little orange-colored post card I sent all my friends for the last Census. It is a very good April Fool's joke. It has the important merits of plausibility and credibility. Nobody receiving my little card had any doubt it was an official notice. It resulted in confusion, almost endless, but not in jail. Example B

You are a music critic. For April Fool's you write that the English horn was ghastly and the horn player should be replaced. You think it was funny, but there is no response.

Question: Why did this prank fail? Because nobody knew it was a prank.

All English horns make all listeners say the horn player should be replaced. So the joke fails, for when the complaint is obvious, there is not wit and no amusement.

You are a woman living with a friend. You say to him, "You should do something about your weight." You mean it as an April Fool's sally and are surprised when he packs his bag, takes both the canary and the springer spaniel and is not heard from again.

Question: What specifically waswrong with this quip? Well, first of all, it was probably justified and that is always a bar. Second, the woman did not really want her friend to move out, and should therefore not have said the one thing that will guarantee a male exit. All too often an April Fool's quip is self-destructive, which is not the point at all. Example C

You answer the phone and some yoyo asks if this is Maryland Amalgamated Savings Bank. You are annoyed, as usual, but what do you do?

You say yes, Barkingham speaking. The caller asks for information. You say:

"All our suburban branches offer $100 gift certificates, redeemable at any of 12 Washington and Baltimore department stores, to any depositor who appears to transact business today." There is no point passing up excellent pranks that fall into your hands, merely because you did not think them up.

You are a man living with a friend. She says, after a rather unpleasant scene in which both of you manage to hurt each other:

"You know, Cletus, sometimes I wonder if I hurt you unintentionally. We all have little faults we don't even notice."

Warning: Do not, under any circumstances whatever, rise to this. It is all right (or at least it is not permanently disruptive) to lose your temper and inquire when the hell she is going to learn to etc., etc. But it is always ruinous to confide, when asked, what her most infuriating quirks are. If you say:

"Gee, Cream, there is one little thing. You know that cackle your mother ends every paragraph with, well you do the same thing on the phone."

Never offer criticism except in a blind rage. Keep that in mind when planning pranks today.

You suspect the prankee is sufficiently zonked on Valium and astrology that no prank will work. What do you do?

Make new friends or, for that matter, new enemies.

It is unfortunately true that for an April Fool's prank to work properly, the prankee must have a latent or vestigal or residual element of sense. Do not waste further time on the hopeless.

An April is known by the fools it keeps, and not since the birth of Harding has the nation faced such a chancy holiday as this day of grace in 1980.

But just remember that, in general, almost anything purporting to be a government notice will be readily swallowed. And be especially careful to avoid direct conversation with persons close to you, and banish forever the temptation to begin any talk with "Now that you mention it . . ."

Finally, it is off-limits to promise the dog a walk and then say, "April Fool." Stick to humans.

If even the most carefully laid prank does not work out, there's always next year. If the prank boomerangs on you (it's been known to occur), well, better an April Fool than no fool at all.