Hi, i have chinese friend and he want to invite me. How should the invitation letter and bank statement be?

Hi, i have chinese friend and he want to invite me in october 2011. so please tell me what kind of invitation letter i needed from him and what information mention on letter? letter will be on simple paper? i will visit him for less then 20 days so how much money i show in my bank statement ? and what is time period of bank statement? please help me in this regards. thanks