FYI, lovely foreigner!

Passport

Obviously you will need to have a passport to get into the US. Two things, first make sure it is up to date. The passport must be machine readable (http://travel.state.gov/visa/temp/temp_1305.html) Second, make sure that it will not expire during your stay, that will cause all sorts of problems. If this is the case renew your passport before applying for your visa.

Visa

Even if you're just visiting the US for a very short time you will need a visa. Make sure to check the website of US Customs for up to date information on the subject. What visa is required of you not only depends on your purpose of the visit, but also the extent of your stay. Some examples are B1 and B2 for Business and Pleasure, J1 for temporary visits such as exchange student stays, and F1 for students attending school fulltime.

Note that if you are from any of the 35 countries that are a part of the Visa Waiver Program you will not need a visa for stays less than 90 days (for the full list of the countries: http://travel.state.gov/visa/temp/types/types_1262.html#2)

In any case always make sure that you do the research EARLY! Good luck.