If someone was planning to hijack a plane, fly it somewhere remote and hold the passengers hostage until that someone got what he/she wanted, these are the 10 steps I think that someone would had probably taken :
1. Establish contact with a group of people who could help in securing a location where the plane could be diverted to without attracting the attention of the international authorities. In this case somewhere in Central Asia should be the best place to hide the plane and its passengers due to the less than strict security of the airspace in many parts of the areas there and the vast plain landscape.
2. Training on how to fly the aircraft and switching off instruments used for tracking it. This can be done by someone who is already well experienced with flying an airliner. Additional training on the intricate maneuvers once the hijacking was done could be carried out using a simulator, which could be built at home.
3. For a plane bound to China, the exact moment best to hijack it is when it is flying across borders, let say between Malaysia and Vietnam. All tracking instruments should be shut down at that point and the plane be maneuvered to the other direction, and in this case to the West.
4. To avoid detection by ground based radar, the plane should be flown very low and the best route should also be between borders such as the Malaysian and Thailand border to avoid the possibility of interception by military aircraft of either countries. Even if Malaysian and Thai military detected the aircraft, they would probably hesitate to scramble their fighter jets to intercept it as there would be a high probability of encroachment into each other's air space.
5. Once passed the landmass of northern Malaysian peninsular, the plane should be diverted north towards Myanmar, perhaps the country with the lowest degree of airspace security in the region.
6. Again the best route to fly the plane as it entered the airspace above the Asian landmass again should be between the borders of either Myanmar-Thailand or Myanmar-Bangladesh with the former being the better choice The chances of a military interception should be low by doing so.
7. The next path should be again flying relatively low across the small countries such as Nepal and Bhutan close to the Himalayan range, and once again the flight path should be close to the borders between these countries and China to avoid military interception. The plane should look unthreatening despite being mysterious as it was flying along the boarders instead of across the borders.
8. Once the plane enters the Central Asian region it should be heading direct to its destination, a secluded abandoned airstrip big enough to accommodate a wide-bodied aircraft. Once landed the passengers should be transported to a safe house by the group which had in the beginning been arranged to handle the matters from then onwards.
9. The plane on open field should had been camouflaged to avoid it from satellite detection.
10. Secret negotiation to be carried out with the country with the most nationals onboard the plane. Details of the deal would only be known to the world after the hostages were released.