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Mistake #1: You go all in on gray—without a plan
Whether you're letting your gray hair grow out because you're courageous, rebellious or just exhausted by the tedium of coloring, it can be a gorgeous look that might just change your life. One thing to watch out for, though: The texture of your gray hair is probably not the same as the texture of your former color, so you'll need to care for it in a different way. Many grays are wiry and dry, yet can look youthful, shiny and sleek if you give them the proper attention. Shai Amiel of Capella Salon in L.A.'s Studio City recommends first sitting down with your hair stylist and assessing the grays: Your hair might be lacking elasticity (protein treatments can help), or moisture (try a hydrating mask). You may also want to treat your grays with a clear gloss to seal the cuticle layer for added softness and shine.

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Mistake #2: You get weekly blow-outs.
We hear you: The rapid expansion of blow-dry bars is pretty great. But it's easy to get hooked, especially when the salons offer hard-to-resist, money-saving packages. Regularly exposing your hair to high heat via dryers, flatirons or curling irons isn't healthy for your hair at any age, because it creates air bubbles within the hair shaft that make individual hairs more prone to breakage, and the longer you do it, the worse it is. Amiel says repetitive styling methods definitely weaken hair. After awhile you'll likely notice that your hair looks thinner or that strands break more easily than they used to. Take some time off from regular blow-outs and let your hair air dry sometimes; and if you do use heat, try to stick to the medium setting (which is usually around 200 degrees).
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Mistake #3: You have an all-one-length cut.
Without layers, your hair won't have that magical, youthful quality that stylists call "movement." Long layers remove weight from the bottom half of your hair so your style can swing and bounce. And while blunt edges accentuate lines in your face, layers have a softening effect. Consider side-swept bangs if you want to make your face look a bit rounder and your cheekbones stronger, says New York City hairstylist Eva Scrivo, author of Eva Scrivo on Beauty: The Tools, Techniques, and Insider Knowledge Every Woman Needs to Be Her Most Beautiful, Confident Self.
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Mistake #4: You have shelves full of styling products.
If you're using more than one styling product in an effort to make your hair look fuller, your plan may be backfiring. "Mousse and gel and hairspray can give the hair lift for a few hours, but they also make it look stiff and sap its shine—a very aging combination," says Scrivo. If you have a well-layered haircut that's not too heavy at the bottom, you won't need to load up on styling products to achieve volume. One dollop of lightweight mousse will do the trick; once hair is dry, use a drop of silicone serum to add shine.
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Mistake #5: You're very blond.
Your skin loses color with age, and over-bleached hair compounds that natural washout by draining the warmest tones from your complexion. Instead of going all-over blond, try a darker base color with golden strands woven throughout, says New York City hairstylist Lisa Chiccine. When you talk to your stylist about highlights, ask for warm colors like butter and honey; avoid cool, ashy tones like platinum and beige, which can make skin look tired and sallow.
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Mistake #6: You have dry, frayed ends.
As you get older, your hair loses not only pigment but also its ability to retain moisture. Keeping it smooth and glossy—hallmarks of youth—requires a little more effort. Do a deep conditioning treatment at least once a week, don't shampoo more than every other day, and get frequent trims to avoid split ends.
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Mistake #7: You have a deep, dark hair color.
Solid black or brown hair can highlight shadows on the face, drawing attention to lines and bags. If you're fair-skinned, a dark hair color also accentuates the contrast between your hair and scalp, which makes thinning more noticeable. A few highlights around the face and at the crown of the head add softness and make a dark hair color appear more natural. "You don't want to look like you're wearing a wig," says Chiccine. Her rule of thumb: Don't dye your hair as dark as it was in your teens and 20s; a shade or two lighter will be more flattering in your 30s and beyond.
long lasting makeup tips

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Mistake #8: Your hair is super-straight.
A lank hairstyle makes your face look long and drawn. (Plus, if you have naturally wavy or curly hair, the hot tools required to achieve straightness leave your hair dry and dull.) If you have naturally fine, straight hair, ask your stylist for long layers and comb a lightweight mousse through damp hair from roots to ends before airdrying or blowdrying (avoid heavy styling creams or serums). If you blowdry, use a round brush to create soft curls at the ends of the hair; setting dry hair with Velcro rollers will also create softness and add volume to offset any drooping in the lower face.

Next: Ken Paves: 5 ways to get the best hair of your life