Generally speaking, China domestic trains start to check in 30 minutes before departure. So it is compulsory to arrive at the rail station at least 60 minutes before departure. In major cities, especially Beijing and Shanghai, rail stations are large and busy; it may take a while to find your train. Therefore, it is recommended arriving at the station well in time. In the case you are taking a train during spring, rush hours or holidays, you are advised to arrive two hours earlier.
Hereafter are the basic steps for train boarding.
You might be requested to show your ticket and passport when entering the rail station. There are security checks (including X-ray luggage checks) at the entrance of each railway station, where your baggage will be checked. Once you put your baggage on the machine, please go to the other side and fetch them quickly in case that your baggage is taken by others either by mistake or on purpose.
After you enter into the railway station, you should find the electronic departure boards and check which waiting room is the appropriated one. In some big cities, departure information is in both Chinese and English. In other cities it may be in Chinese only, but you can easily find your train if you know the train number and departure time or you can ask a staff for help if you cannot find it. There may be 2-4 trains using one waiting room.
In most cases, check-in starts 30 minutes before the train's departure when it is the starting station. But sometimes G, C & D trains may start check in 15-20 minutes. When your train starts the check-in process, you should stand in a queue and go through the ticket barrier. At the barrier you need to show your ticket and passport. About 5-10 minutes before departure the barrier is closed and the check-in will stop.
The train number and the carriage number are shown outside the train clearly; therefore it is easy to find your carriage. There is a railway staff at the door of each carriage to whom you are requested to show your ticket.