Key to a good nap in the middle of the day at work:

Make sure the car is parked in the shade, preferrably in a parking garage so that you don't have people walking by the car and gawking at your mangled form on the back seat and calling the police because they think you're a dead body (perfect way to ruin a good nap). Pack a pillow or an extra large jacket, something for head cushionage, and make sure your legs are level with your head, otherwise all the blood will rush to the toes and your ankles will swell like a pregnant moose. Roll down at least one window, else risk asphyxiating yourself on your own farts. Don't look all innocent, we all fart in our sleep.