What is the perfect route from Mianyang, Sichuan to these three destinations, and how to arrange transportation by plane and train?

For reference: Mianyang train to Pingliang, Pingliang bus to Longde, Longde bus to Guyuan, and finally Guyuan train back to Mianyang. (or vice versa)

Use your favorite method from Mianyang to Chongqing, then I take the plane to Guyuan, take the train to Pingliang, and then take the train to Xi’an