Elong and www.ctrip.com
are the main online travel booking for China.
They do both have english version.
Very easy to check price and schedule for the domestic flights of all airlines.
They also give the aircraft type for each flight which is very helpful.
Reliable hotline in english (very rare in China...) for foreigner travelers who want to book from overseas.
Prices are very flexible and vary according to the yield.
I often buy my tickets lastminute and get very good deals
The best way would be to check the price and schedule online and buy ticket from your hotel business center by giving them the flight details and price (world class hotels in China all have this service) while you are in China.