if I travel myself not with tour agency what the document I need to prapare for tourist VISA to China?

Dear Sir,

I am Thai citizen and work in Laos. I would like to travel in China on my holiday.
I would like to know if I travel myself not with tour agency what the document I need to prapare for tourist VISA? I won't have invitation letter, so what should I use instead?
What kind of application form I need to fill in? and where can I download the form?

Thanks in advance.