Some Hollywood secrets, like how J.Lo kept that Versace dress up all night or why Gwen Stefani's hair has stayed both platinum and healthy for decades, are unanswerable. But there's one we were determined to learn: how to perfect the art of lining your eyes on the inside. It's the key to naturally full-looking lashes and the final touch to any smoky eye--but it's surprisingly hard to execute! So we asked two artists, both of whom have mastered the look on celebrity faces, for their secrets. Allison Williams popped up at the New York premiere of season two of Girls with eyes to match her Altuzarra dress. Makeup artist Julie Harris lined Williams' lash line with Cargo's Color Palette ($30) in Baja for a golden glow, before filling in her upper and lower waterline with Cargo's High Pigment Pencil ($16) in Black. "I applied the pencil a few times to give it staying power," Harris says. "And I cleaned the inner corner with a Q-tip so that the pigment doesn't sit in the inner corner." While liquid eyeliner veers into dangerous territory--it's slippery and harder to control--makeup artist Beau Nelson does favor a gel formula, like Bobbi Brown's Long-Wear Gel Eyeliner ($23) in Black Ink. "Put a bunch on one side of a flat, square eye shadow brush and barely wiggle it, just press it into the waterline," says Nelson, who may have perfected the look on Kristen Stewart at the premiere of On the Road, above. Try Laura Mercier's Flat Eye Liner Brush ($25) for this look. "I also love M.A.C.'s Eye Kohl ($15) in Smolder, but only if you're going to build a smoky eye on the rest of the lid," Nelson added, pointing out that anything that smudges is bound to be less precise. The reality of this look is that once it's done, it's hard to control. "[Celebrities] just have to make it down the red carpet," Nelson admits. So throw your tools in your bag on the way out the door--it's the next best thing to having Harris or Nelson on hand all night.