There are three main ways for tourists to get to Xining, taking a train, taking a flight or taking a bus.
Taking a train to Xining: Due to the construction of Qinghai Tibet Railway, Xining has become the major gateway for tourists who want to travel from Xining to Tibet. The railway connects many major Chinese cities with Xining together, including Beijing, Shanghai, Xi'an, and Qingdao. You can take a train to Xining in these cities.
Taking a flight to Xining: if you want to take a flight to Xining, you need to arrive in the following Chinese cities such as Beijing, Guangzhou, Kunming, Shenzhen, Xi'an, Chengdu, Chongqing, Dunhuang, Golmud, and Urumqi.
Taking a bus to Xining: buses are available to the public in some major cities or towns such as Golmud, Dunhuang, Lanzhou, etc. You should have a better understanding of the local condition before taking this away.