1. School letter to prove you have an vacation, your parents' proof of income and assets.
2. It depends on how soon you can schedule the interview. But if approved, you will receive your visa within 14 days.
3. You fill out the form here:
https://ceac.state.gov/genniv/
The form (as well as your photo) will be transmitted to the U.S. Department of State database.
It is suggested you can apply 6 months in advance.
4. Apply one then.
5. Being stupid (For real - the #1 reason for visa denial is being stupid). Remember, you apply the visa to travel. Then you have to convince during the interview that you go there for travel. How you want to prove it is up to you.
For visa application in detail, you can go to:
http://chinese.hongkong.usconsulate.gov/niv_apply.html