There are currently 3 direct buses from Kunming Nanyao Bus Station to Yuanyang Xinjiezhen everyday. The Express departs at 10:40am and arrives 6-7 hours later. The scruffy sleeper buses leave in the evening and arrive in early morning of next day. The alternative is to arrive Yuanyang Xinjiezhen from Kunming via Gejiu or Jianshui (also at Kunming Nanyao Bus Station).

Kunming-Jianshui-Yuanyang Xinjiezhen
Kunming to Jianshui: 4 hrs (220km), buses leave every half hour between 7:30 to 16:30, then 17:10, 17:55.
Jianshui to Xinjiezhen: 3.5 hrs either by a direct bus at around 8:00am or the Jianshui-Lvchun bus at noon between 11:30~12:10 (pass through). Or else, you need get to Nanshan(Yuanyang new city) and then transfer to Xinjiezhen, which is much complicated.
Kunming-Gejiu-Yuanyang
Kunming to Gejiu: 4-5 hours (300km), normal buses (about RMB80) departure between 7:30 -19:00. Express bus (about RMB100): 8:40, 14:20, 15:40
Gejiu to Xinjiezhen (Yuanyang old town) 3 hrs / RMB45

For leaving, reverse of getting there except that one can even catch a direct bus to Zhongdian (Shangri-La) from Gejiu.

Getting Around
To enjoy either the sunrise or sunset views at Yuanyang Rice Terraces, you will need to charter a vehicle, as the public transport which consists of either motorized tricycles, mini buses or vans do not run so early or till so late. The rental of a 6-seat van is RMB250/day, 5:30am to 8:30pm, no matter whether you return to hotel for a rest during 12:00 noon to 4pm when there is not  so much to shoot due to the intensive sunlight.