John Dunning's "Booked to Die," first published in 1992, is an ironic example of what's happening in the world of book collecting.

The protagonist of "Booked" and its sequel, "The Bookman's Wake," is Cliff Janeway, former Denver homicide detective turned rare book dealer - which used to be author Dunning's occupation.While solving murders, Janeway tosses out tips on collecting and prices. He observes - with more than a little dismay - that some works by horror writer Stephen King are now commanding as much, or more, as classics by Twain, Steinbeck and Hemingway.

So what's happened to the price of a "Booked to Die" first edition? In just six years, it has skyrocketed to $850 - which could also get you a Twain, Steinbeck or Hemingway, a Faulkner or even a Dickens.

"When people think of collecting books, they think they must be old to be valuable," says Dallas bookseller David Grossblatt. "That's not true. `Cold Mountain' (the Civil War novel by Charles Frazier) came out last July. A first printing is now valued at $150."

Firsts of "Midnight in the Garden of Good and Evil" by John Berendt, published in 1994, also bring $150.

But some of the biggest, quickest jumps in book values in recent years have been among whodunits. Besides Dunning, other mystery writers whose early efforts now command staggering sums include Tony Hillerman, Sue Grafton and Patricia D. Cornwell.

"Forty percent of the books that are read and collected today are mysteries," Grossblatt says. "Next is fiction-literary books, then history, science fiction and, sadly, then the classics."

But before you head to your bookshelves to pluck off your fortune, booksellers caution that the highest book prices are paid only for true first editions, and they must be in mint condition.

"As the real estate mantra is location, location, location, the bookseller's is condition, condition, condition," says Tom Keener, an antiques and collectibles dealer who teaches a course on evaluating books.

"Dust jackets are absolutely critical to the value of a book," he says. "But often you'll go into a home and find the books are jacket-less. `Our decorator said to take them off,' is what you hear. I say, fire that decorator."

The jacket should be clean, unfaded and untorn. "The price should not even be clipped," Keener says.

As for the book itself, the No. 1 rule is, "Do not write in them!"

Unless you are someone famous, simply putting your name or a book-plate inside a book can knock as much as 60 percent off its value, Keener says. Birthday greetings or other messages are strictly taboo.

A book autographed by the author brings a premium - but don't ask for a personal inscription.

"From an egotistical point of view, it is nice to have a book inscribed to you by the author, but it diminishes the book's value," Keen-er says.

Valuable books should be kept behind glass (in closed bookcases) to protect them from humidity, air pollution and insects, Keener says.

Also keep books away from windows (sunlight can fade the spines), and don't tuck newspaper clippings or other objects between the pages. The clippings will yellow pages; bulky items can bend the binding.

If you actually read a first edition, you should do so very carefully, dealers say.

"Since condition is so important, it might be best to stick it on a shelf and buy a drugstore paperback to read," says Dick Bosse, owner of Aldredge Book Store in Dallas. "Or go to the library.

"With a thick book like Larry McMurtry's `Lonesome Dove,' if you read it once, you've probably pulled some threads (in the binding), and it's no longer mint."

Publishers use many different ways to denote their first editions and later printings, so there is no single rule for spotting firsts. Before you spend the bonanza you're expecting from your pristine copy of Sue Grafton's "A Is for Alibi," you might consult a book on collecting or ask a dealer to verify its authenticity.

To be avoided (if you're buying as an investment) are book-club first editions. Ways to spot these include 1) no price on the book jacket and 2) a tiny indentation, called a "blind stamp." This indentation is usually on the lower right corner of the back, but it may also be found on the spine.

Identifying some firsts requires almost esoteric knowledge. Fred Holt, a dealer at Love Field Antique Mall, has a first edition but second printing of Hemingway's "For Whom the Bell Tolls." Only the well-informed could identify it as a second printing - the lone clue is that Hemingway's name appears under a back-cover photo, the name wasn't included on the first printing.

The price difference is huge: A first printing might bring $400 or $500, Holt says. The price on his second printing: $39.95.

Book collecting "is not an exact science," he says, though some clues are obvious, "such as a dust jacket blurb that mentions a book written after the supposed first edition."

Holt's factors of what makes a book valuable:

-Somebody has to want to buy the book, the more somebodys the better.

-The book has to be somewhat scarce.

-It has to be in good shape.

-Finally, it has to meet all of the above points.

He says a new category of collecting is "early technology - prior to 1950 - especially aircraft books."

Children's books also are popular. "Most people buy the books they read as a child," Holt says. "They are mad at their parents for throwing them out, but I always say, if (the parents) hadn't thrown them out, I wouldn't be in business."

Some collectible books that he frequently finds in Dallas homes include Douglas Southall Freeman's four-volume "R.E. Lee" and two-volume "Abraham Lincoln." Each set is valued at $240.

Bosse, who has owned Aldredge since 1957, says one reason 20th-century books have become so collectible is that many older books "have been scarfed up to fill the shelves" of new colleges started during the Johnson administration. "There's no way you can fill in a Shakespearean collection today," he says.

"But people want to collect something, so you see a great deal of activity in such writers as Tony Hillerman and Sandy Cisneros - because they are accessible and within the price range of most people."

More authors are collected than subjects, Bosse says, though there is still high interest in Civil War and World War II books (but little in WWI or the Spanish-American War).