i am american citizen, my visa expires Nov. 21, 2014.planning to travel in November what do i need ?

You are in USA, now?
If so, you cannot renew your current one in USA. Actually, if you can enter China before Nov. 21, you can stay in China for a period the stay of duration requires.

If you are in China now, you can go to the local Exit-Entry Adminstration Bureau for renewing. The required documents are different based on different types, so you may need to tell me your type to know the needed paperworks.