When you're going darker, use a semipermanent formula the first time around. If you like the shade, wait until it fades and then apply a permanent version. Start in the back and save the strands around your face for last. The front pieces of your hair tend to be porous (due to daily wear and tear), so they'll absorb more color than the back and underside.
When you're lightening up, look for a permanent shade that has the words neutral, beige, or ash in the name to prevent your hair from looking brassy. Start in the front and work your way to the back so the pieces around your face are the brightest. If you want to go even lighter, you can use a highlighting kit afterward. Warning: Dark brown hair can sometimes turn orangey if you lift it more than two levels, so go to a pro if your natural base is darker than a medium brown.
"When you're touching up your roots, whether you've lightened or darkened your hair, you should apply color to the regrowth only (the part closest to your scalp) so you don't overprocess your locks or end up with an uneven hue," advises Marie Robinson, senior colorist at Sally Hershberger Downtown Salon, in NYC.
Time it right. Start your timer as soon as you begin applying the formula and don't leave anything on for more than 30 minutes or you'll cook your hair, warns celebrity colorist Rita Hazan.
Sexy secret: Go streaking. The trick to getting hot highlights is all in where you place them. You'd never get ruler-straight, evenly spaced streaks naturally from the sun, so don't layer them on that way. At home, keep highlights between 1/8- and 1/4-inch thick, and don't overlook the hairline, since those pieces will brighten your face.
Protect and preserve your hue. Investing your time and money in a new hue is only worth it if it lasts, which means you'll get more out of the shade if you treat it right.
Avoid washing your hair for about 24 hours after coloring it. When it's time to lather up, opt for a color-safe shampoo and conditioner that contain UV protection, and steer clear of clarifying or deep cleansing formulas, which can strip dye pigments. And in general, avoid shampooing every day to prevent fading.
"Gloss treatments enrich your natural color without depositing any dye. Try an at-home version or treat yourself to the salon experience. Most take only a few minutes to activate, so you'll pay less than you would for a full head of highlights or a single-process color," suggests Robbie Contreras, Color Director at Tela Hair Salon in NYC.