1. Know your limits.
Permanent hair color contains chemicals to open the hair shaft, strip color, and let pigment inside. "You can only go two shades lighter with these, because the formulas aren't strong enough to lift out a lot of pigment," explains colorist James Corbett, Clairol creative director. If you're a deep brunette, pick up a light-brown shade. If you've got medium-brown strands, try dark blonde.
2. Stay cool.
A cool or ashy tone will counteract brassiness, an unwanted side effect of going lighter. Try Clairol Nice 'N Easy Permanent Hair Color 6A/114 Natural Light Ash Brown ($8, at drugstores). And if your hair ever does get an orange tinge, pour some cool black coffee over damp hair, leave on for five minutes, then rinse. "Coffee's greenish-brown tones will neutralize the orange," says Kyle White, lead colorist at Oscar Blandi Salon in New York City.
3. Add depth.
After lightening up, paint on a few face-framing highlights for even more dimension. But don't go overboard—for brunettes like me, a "bronde" (or brownish-blonde) hue, like Sofia Vergara's, looks more natural than pale gold.