It's not often that you wake up and realize your house needs some tropical fish. But when the mood strikes, there's no point struggling against it.

A couple of years ago, two New York housemates got the urge. Did they know anything about fish? Not a chance. They called up a mutual friend. He didn't know anything either. Nevertheless, the two housemates gamely went to the local tropical fish store, where they bought some fish and fish-care paraphernalia.

It was an adventure that was destined to end unhappily. They hadn't gotten the advice they needed, and their fish were out of commission within six months. Was there, they wondered, a larger lesson here?

Not only a larger lesson, but a large book. The two housemates and their friend -- one single, one married and one divorced, all somewhere near 40 -- have produced The Modern Man's Guide to Life (Harper & Row, paperback, $12.95), a thick encyclopedia that aims to give advice and information about everything from making pasta to wearing the right clothes. Except tropical fish. There's not one word about tropical fish.

There are, however, suggestions on the world of work: "No matter how many hours you spend working, your brain won't give you more than six hours a day. You'll notice that if you work longer, you become more distracted and require more rest intervals ... After six hours, you'll be on overtime and running on empty."

On going to the barber: "Once you get the haircut you want -- when you really think it looks swell -- get a friend to take some Polaroids of it. Next time you need a haircut, bring the photos to the barber. If it can be done right once, it can be done right twice."

Approaching women: "The less threatening the environment, the more aggressive you can become. In the produce section of a supermarket, you can use almost any opening line that comes to mind. (In the New York subway, nothing you say short of absolute brilliance will work.)"

Doing the laundry: "Washcloths? Abandon them. You can clean yourself very well using your hands, just like God intended. Washcloths are hard on your skin, and unless laundered after every use, they are simply damp havens for bacteria and dirt."

Aftershaves: "Old Spice is an Oriental scent that seems to be the most universally appealing fragrance to women. Maybe it reminds them of their fathers. In any case, it is the least pretentious of the most widely available scents."

And for the modern man who is hungry and lost in the woods, there's a perfectly disgusting illustration that quite graphically tells how to dress a rabbit without a knife.

Unless you're planning on getting lost in the woods, this last item is one you might want to live without. In fact, not all of the 3,000 bits of advice here are useful. Some are too vague ("Never buy anything ... from an antique or junk shop if there are more than three things wrong with it") or too subjective ("More than half the women in the country do not like Ms. as an honorific"), while a couple are just plain goofy (to save time in the supermarket, "scout the aisles for a no-nonsense mom or a sensible grandmotherly type pushing a full cart. When her back is turned, make off with her selection of groceries"). But the vast majority are reasonable and helpful.

All this information was solicited from the friends and friends of friends of the three coauthors. This wasn't as easy as it sounds. Denis Boyles, one of the coauthors, says the entries unfortunately often fell into two different categories: "Either they were painfully obvious -- 'Say thank you when you receive a gift' -- or so obscure, so obtuse, that it was difficult to even validate them. Someone sent us something on poison ivy that said immunity involves eating it. I don't know about you, but I'm not going to test that out."

A portion of the information here could be found in reference guides of one sort or another, including such mundane entries as removing stains, painting interiors and identifying trees by their silhouettes. "The real gold in the book," maintains coauthor Alan Wellikoff, "is in the semi-secret rules for living that we have throughout. In the course of our friendship, we noticed a category of information between what is commonly known and what is too embarrassing to reveal."

As an example of this type of information -- the kind that is mythically thought to be passed on from man to man after they've downed a beer or three in the local bar -- he says, "Women provide you with a window of opportunity when they're interested in you. If you don't act during that time, they're lost to you forever ... That's the kind of thing we wanted the book to be a compendium of: these little tidbits of wisdom that men don't usually share unless they're intimate friends."

This is folk wisdom, of course, and who knows whether any of it is true. An example from the book -- these tidbits frequently seem to be about the opposite sex -- goes like this:

"Women hate so-called 'new age' men, despite the media's protestations to the contrary. The idea of a man sitting down and weeping about his difficulties on the job or shedding tears of joy at the thought of a Saturday night dinner date is enough to make most sensible women puke."

Take it for what it's worth.

Men have never been known for buying self-help books. "From what I understand," says Wellikoff, "half the people who buy our book are women, to give to their unruly boyfriend or husband, or perhaps to get some insight on how men behave." If so, that opens the question of who will buy The Modern Woman's Guide to Life, which is currently in preparation. Will men buy that to give to their unruly girlfriends and wives?

No, says Karen Kriberney, who at this moment is holed up with her two coauthors in a Baltimore hotel, racing to meet the deadline for finishing the manuscript. She sees the primary audience for her book as being the sex for whom it is written.

While reluctant to categorize something that isn't completed, Kriberney says there will be correspondingly less about men in her tome than there was about women in the guys' effort. Furthermore, "we've had a lot of very practical responses," she says. "In Modern Man, there's a lot of philosophical material. We don't seem to be heading that way."

Yet why does either sex need to be told anything -- whether factual or subjective -- in the first place? "Mothers simply don't pass this stuff on to their daughters anymore," explains Kriberney.

As for men, "this generation may be the first that doesn't have an ability to gain avuncular lore," speculates Boyles. "There's a confused perception of what to do. For instance, there really are stalking this planet 25-year-old men who think they're supposed to cry on cue and exude sensitivity to an inappropriate degree, just because they think that's what women want."

Don't do something because you think that's what women want, is the unspoken thread running through The Modern Man's Guide to Life. Don't do anything because it's what you're supposed to do. Do it because it's right.

"This is a Boy Scout handbook for grown-ups, and therefore very square," says Boyles. "Modern men, more than ever, need to rely on old-fashioned common sense, not only when buying used cars, but when dealing with women, children or jobs."

Moreover, he says, "the book is written in opposition to something we call the modern conceit. The latest idea, we maintain, is a bad idea. Take the notion that it's no longer appropriate to hold open a door for a woman, because that kind of mannerly and courtly behavior has undesirable overtones. The fact of the matter is, you should always hold open a door for a woman, and that sort of philosophy is true for most of life." (Significantly, Kriberney says the woman's guide will reflect this same attitude.)

In the end, though, you're still on your own. "We're not liable for any consequences whatsoever arising from the use of this information, and neither are our contributors," the book states. "Advice is never a substitute for experience."