International applicants have some extra requirement when applying to American universities. International applicants will have to focus more heavily on proving that their credentials are true. For example, in China there are fraudulent companies that fake applications and submit them to various schools. American schools are learning to recognize such applications and will ere on the side of not accepting a student they suspect of purchasing such an application. Being authentic is important to colleges and so sometimes mild imperfections are a sign that you are a human and not a computer generated applicant.
International applicants sometimes overemphasize test scores and academics (although both are important) and deemphasize extracurricular activities and the college essay. It is important to remember that only the latter two show your passion and initiative.
The biggest difference between domestic and international will be the TOEFL examination, which measures a test-takers English comprehension through listening, reading, speaking, and writing sections. The TOEFL is important to show colleges that you will be able to effectively communicate and interact while on campus. You should try to take it as early as possible, and the best way to practice is through immersion (watching TV shows, reading books, and visiting English speaking countries).
Another key thing to remember is that you have to make sure your application material is sent in English to the colleges you are applying to. Also, often, applicants will be able to interview through a computer program. All applicants who are offered an interview should take one! Some top universities have alumni in different countries and they will set up meeting to interview. Again, do not let an interview opportunity go.
The biggest difference between international colleges and American colleges is the liberal arts factor. Most universities allow students to pursue a broad range of classes and subjects. Even pre-professional programs (pre-medicine, pre-law, etc.) allow students to take classes in other subject areas. If you are applying to an American college, you should make sure you understand the difference in college education. If that is the type of education you are seeking, pursue your application.