Rail travel in China is a highly recommended way to move about. It is a fast, affordable and comfortable method of transit between most cities. In general there is always an availability of tickets even up until departure time, but one should note that during certain holidays like the Chinese New Year, tickets sell out fast. To combat this it is good to know that rail tickets for any particular date start being sold 12 days in advance. If you want to be assured of getting a spot even before you arrive, write your hotel concierge. Many will be willing to go and get the tickets for you charging a basic fee for their transit to the train station. All that is needed is the ticket info, a scanned copy of the passports of those traveling and a credit card number for guarantee.
In addition one can buy rail tickets at any rail station even if traveling between two completely different stations than the place of purchase. Tickets can be purchased online too, but the official train site is only in Chinese. Other English language sites will charge a fee for helping you reserve. When buying tickets one must understand that proof of ID is required, thus a foreigner (anyone without a state issued Chinese ID Card) must purchase from the ticket window, not from a machine. Ticket window purchases cannot be made with a foreign credit card.
It can be challenging to purchase the tickets relying on your own pronunciation of the destinations. Persons at the ticket window generally do not speak English. For that reason it is imperative that you ask a hotel concierge or Chinese speaker to write down your ticket request for you in Chinese. Request them to write at least the date, destination and class of ticket you wish to purchase. If you have a particular train number or time you wish to catch have them include that too.