The 1200 kilometer route from Xining to Chengdu through the traditional Tibetan region of Amdo has become quite popular in recent years. This route passes through several amazing Tibetan towns that are home to some of the most important monasteries in Tibet. This route also goes through some excellent nomadic regions. In fact, some of the best nomadic areas in all of Tibet are found in this area. This route can be done using public transportation, though if you have the money, hiring a private vehicle is much better as you can get to the more remote nomadic areas much easier and can see the areas between towns that others rarely get to see.
You can see a recommended 11 day itinerary and photos at http://www.thelandofsnows.com/overland-from-xining-to-chengdu/ . If you have any questions about this route or any other questions about travel on the Tibetan Plateau, email Losang at firstname.lastname@example.org .