We followed the advice of several others and got a guide to trails in the area from the NPS office, just outside Williams. The directions were easy to follow and necessary since the fire roads are not well marked (or just plain unmarked). We hiked from the Sycamore Rim vista point and headed towards the Sycamore Falls, but we did not get to the falls after about 2 hours of slow hiking with a cranky teen. It was a hot day and there is no water and there were lots of biting flies/mosquitos, so be prepared with water, bug spray, a hat, sunscreen, and good hiking shoes. The trail is easy to follow and well-marked, but quite uneven and studded with rocks.
Another trail I would highly recommend is Keyhole Sink, off exit 167. Directions are on the same map and the hike is quick and easy, and leads to a beautiful little canyon with stone drawings from 1,000 years ago.More