Let the hemlines go up or down, for most people the most remarkable thing about clothes these days are the price tags. The news from the Consumer Price Index -- Washington prices for women's and girls' clothing are up 12.4 percent over last year -- was hardly a shock.

It is also no surprise that the emphasis of current fashion books is on buying wisely and on stretching the uses of clothes already owned. With designers' confusing messages about lengths, colors, shapes for the season ahead, the best guides consider the wearer, not the trend.

One of the best of these manuals is Hot Tips: 1000 Fashion & Beauty Tricks, by Frances Patiky Stein, designed by Rochelle Udell (G.P.Putnam's Sons, 193 pages, $12.95).

The authors are insiders, long experienced in the fashion business. Stein -- a former fashion editor at Harper's Bazaar and Vogue, vice president of Halston and director of the Calvin Klein design studio -- now works in Paris researching and developing Chanel accessories. Udell, who heads Calvin Klein's advertising, is a former art director of Vogue, House and Garden and Self.

Their book, stresses Stein, does not attempt to make you look "in fashion." Rather it is "about building a wardrobe around pieces . . . with a relationship to each other, a consistent style and mobility so that a few pieces become numberless, interchangeable looks -- and looks which work for you."

Starting with a bare you in front of a three-way mirror, the guide -- amply illustrated by Stein -- touches on everything from your closet to your haircut to 24 ways to wear -- and preserve -- a sweater.

Their test for your closet: "What tones do you notice first? If you answer red," says Stein, "you really have to do a rethink. The classic neutral tones are the key to a skeleton wardrobe--a foundation. They serve as a painter's canvas . . . you embellish upon them."

For the woman who has been caught up in changing jacket lengths, Stein offers relief: The ideal jacket, she claims, just covers the derrie re where the legs begin. "Nothing looks worse (unless you've an extra-perfect body) than a jacket hitting mid-derrie re -- it's like arrows pointed to the wrong place."

Among other suggestions:

* Avoid bust darts in anything, especially a shirt.

* Remember that pale colors cast the most flattering light on your face.

* Watch for a proportion of more skirt than jacket, for balance and the illusion of a long narrow body.

* Tone stocking colors to shoes, not skirts, for the effect of a longer leg.

* Keep hair off shoulders. "Nothing drags the eye down more than hair that is too long."

* Use pads or epaulets and horizontal patterns if you tend to slouch.

* If you have a big bosom, wear open-neck sweaters, blouses, dresses to create a vertical effect. "Always small, invisible buttons."

* To give the illusion of a narrower shoulder, have your tailor adjust set-in sleeves by moving them in toward the neck by 1/8-inch.

* Camouflage a protruding stomach with side pockets and side gathers, and wear skirts and pants on the loose side.

* Never wear anything that cuts the leg. No ankle-length pants. No cuffs. No mid-calf skirts. No knee socks. No ankle-strapped shoes. No shoes with bows at instep. No short socks and sandals with skirts. No Bermuda shorts, mini-skirt, etc.

* Look for straight-leg pants. The illusion of a straight leg is best achieved with pants that taper an inch or two from knee to hem. The slimmer the trouser leg the better.

* Reveal a bit of leg with button-front or front-slit skirts to "lengthen" the look. "Your legs can never look too long."

* Never buy a skirt with a binding waistband. "Aside from squeezing (and feeling terrible), a tight waist instantly knocks off the correct fit of skirt."

The ideal skirt length, says Stein, is 1 1/2 inches below the knee, skimming the back of the leg where the calf begins to curve in. "Skirts that are too long drag, too short, and they cut the legs and make them look shorter."

Other ways to make the most of what you have:

* Avoid the overhead light when applying makeup: It casts distorting shadows.

* Always match foundation color to skin color of neck (not hands, as is often done at makeup counters). "You should never be able to notice your makeup -- only its effect."

* For evening, dab your lip color at the center of upper eyelids -- to "centralize and balance" everything.

* Set your hair before getting into bath or shower; the steam makes it curl more quickly.

* For a quick refresher, rub ice cubes lightly over face, neck, back of neck. "Don't forget wrists."

* At the first hint of accessory overload, "unload!"

Remember that the shorter you are, the shorter the muffler.

* Never buys shoes early in the day when your feet are their smallest.

* If you plan to wear rubber or vinyl boots all day, wear thin cotton socks over your stockings.

* Always buy storm boots one size larger so you can wear wool socks underneath. Tight boots are colder.

* Skip the flat-shoe fashion if you have heavy legs.

* Never file nails into corners, it weakens them.

* If uncertain about your choice of haircutter, watch how he works on other clients. Test him on the first go-round with a "trim," not a total restyling.

* For temperamental skin, steep two teabags, cool and then dab face with bags for five minutes. Rinse.

* For dry, itchy skin, wash with superfatted soap and dab with milk. Leave on for five minutes. Rinse.

* Keep pictures around of slim, great-looking people, plus one fat one.

* Buy the best you can afford.

Throw away all wire hangers. "They ruin clothes."