Fashion is ever-changing, but elegance is eternal. In no area is that point clearer than workwear style, where certain "rules" have held firm for decades (face it: It's never been appropriate to wear something wrinkled, messy, or too revealing for a nine-to-five gig).

For further proof, we're looking to Hollywood's most iconic costumer ever, Edith Head, who knew, oh, just a thing or two about how to pull off a sophisticated look (ahem, that can happen when you're the go-to stylist for Grace Kelly, Elizabeth Taylor, Veronica Lake, and Audrey Hepburn). With a whopping eight Oscars under her belt, Head—who was instrumental in giving us all that Breakfast at Tiffany's chicness—understood how to translate silver-screen glamour to real life too. She combined her expert style advice in a signature 1967 study, How to Dress for Success. While certain parts of the book feel uncomfortably retro (like an entire section on getting and keeping a husband—"choose your wardrobe to please him and suit his way of life." Um, no.), the chapter on dressing for the office works just as well today as it did nearly 50 years ago.

Edith Head with Veronica Lake

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Her key advice is everything we'd still advise today. Like they say, classic never dies. Check it out:

Dress for the job you want.

Ever since there have been offices, job-hunters have been encouraged to outfit themselves in a way that would fit in with the overall vibe. It's something Head speaks to within the first 10 pages, reminding readers that there are a lot of differences between someone working in a white-shoe law firm and another logging hours in a creative advertising agency. Both are polished and professional, but the latter will appreciate bold colors or prints in a way that wouldn't fly with the lawyer crew. Figure out what's appropriate for the style vibe of your chosen field and dress accordingly.

Rely on a stable of basics.

If you're just starting out on your career or working on revamping your closet, don't waste any time in feeling overwhelmed. Rather than studying trends and debating over statement styles, invest in the basics and you'll never go amiss. First focus on sleek dresses, suiting pieces, and tailored separates when shopping (basically anything that gives off that Head-perfected Audrey Hepburn sophistication). To get started, check out this list of pieces every woman should own by age 30.

NEW YORK, NY - FEBRUARY 04: A guest is seen wearing a yellow handbag and blue high heels in the streets of Manhattan during New York Fashion Week: Men's Fall/Winter 2016 on February 4, 2016 in New York City. (Photo by Timur Emek/Getty Images)Getty Images

Pre-plan what you're going to wear.

There's no denying the time-saving element, but thinking about your outfit the night before can also help ensure you're as chic as possible. The example Head gives calls to mind late-alarm mornings when you're in a rush to make it to a meeting in clothes, no matter a full-on look (it's "a mad scramble in the morning, wildly pulling things out and dressing like a house on fire"). To avoid, look at your calendar to see what the full day entails and pick pieces that will work for everything. If you're not sure how things fit, try them on before turning in; it'll save you the pain of finding a substitute in the morning dash.

Actually test out at your outfit.

If you're trying on a new outfit or pieces you just bought, don't just pull them on and head out the door. If the majority of your coworkers will see your clothes while you're sitting at your desk chair, erm, sit. Does your hemline ride up higher than you thought? The buttons on your blouse gape open? Look at all your angles to avoid any not-so-nice style surprises.