About an hour and a half east of Flagstaff on Interstate 40, exit at Holbrook and enter Petrified Forest National Park at its south entrance. Stop at the main park visitor center to pick up maps and information about the park's highlights.
The light on the Painted Desert is clearly better for photography in the late afternoon as opposed to the early morning. I prefer entering the park at dawn and spending the early hours exploring the petrified wood areas in the south. Stop by the visitor center and pick up maps, etc and work your way to the Painted Desert by late afternoon when the light becomes warm and the shadows log. Blue Mesa is clearly marked and offers several overlooks as well as a scenic 1 mile loop trail; both offer fine photo opportunities during the "golden hour". However, the park's hours are somewhat limited, closing at 5PM in the winter and 6PM in early spring; thus, the best time of year to take advantage of golden light is early spring. You must be on your way out of the park within an hour of closing; thus, exiting from the park's north entrance will give you more time with your camera since the Painted Desert is quite close to this entrance.