The technical requirements
There are many students that enter college with high GPAs and test scores and realize they don’t know the first thing about how to do the work required of you in college. Hopefully you’ll have professors and teachers who can help you learn, and many colleges and universities have places where extra help can be procured. (like the Writing Center at the University of Wisconsin, Madison). That said, for most people the first semester is a period of “sink or swim”, where you either learn –very quickly- how to do the things they’re asking, or you receive poor grades. Writing assignments have very specific expectations about style and formatting, and when I taught at UW I had international students every semester who failed major assignments because of these technicalities.
Universities in the U.S. are incredibly strict about plagiarism, and students who misunderstand or underestimate these rules end up with permanent marks on their file, noting instances of academic misconduct. Students are expected to write emails and cover letters with a level of formality that is new to most high school students, and many freshmen give a horrible first impression brought about by an ignorance of the unspoken rules. All of these things can be avoided, with some guidance.