If you're on Route 66, take the Kelbaker Road north near Chambless. This will take you straight through the middle of Mohave National Preserve and past Kelso Dunes and the visitor centre, it's tarmac all the way.
Carry on north to Baker (plenty of cheap motels and food places plus the world's tallest thermometer! The Mad Greek restaurant is'nt bad) then take Route 127 or Death Valley Road pretty much opposite the Kelbaker road. After about 60 miles take a left onto Route 178 just past Shoshone (should be sign posted) which runs straight up through the middle of Death Valley past all the touristy bits like Badwater, Devil's Golf Course, Artist's Paletter etc.
Furnace Creek is pretty much in the middle of the Park and has a couple of restaurants, a bar, a few campsites, hotels and the visitor centre.