ANSWER: Be sure to buy a waterproof formula like the Revlon ColorStay Liner ($7; target.com); it's more resistant to smearing. "Eyeliner usually runs when it encounters oils on the skin," says Revlon global artistic director Gucci Westman, who works with Cameron Diaz. Prior to applying, dab an eye-shadow brush into pressed powder (We like Revlon's Photoready Powder, $13; target.com) and gently drag along the lash line to prep the area and prevent smudging. "This helps soak up oils and lock the eyeliner in place," says Westman. And remember: Always apply powder before puttng on mascara, or your lashes may end up getting cakey.