How can I buy train tickets in China by myself?

It's easy to buy tickets yourself at the station, but remember to take your passport with you.

In big cities such as Beijing or Shanghai you should look for the special ticket window for foreigners.

Reservations for the best D- or Z-category express trains open 20 days before departure, but reservations for other trains open 20 days also before departure.  You cannot buy tickets before reservations open.  If the train you want starts its journey somewhere else and calls at your boarding station already well into its journey, tickets may only be available 2 days before departure.  The exact rules vary by city and by train.