Take a look at this:
http://talk.collegeconfidential.com/high-school-life/2055289-faq-high-school-college-prep-base-curriculum.html#latest
Mistakes I have seen people make:
Taking advanced AP classes before they are ready, e.g., taking AP Chem as a sophomore with no previous chem background
Taking DE classes but not the right ones. For a nursing major, you should be taking some science and math not sociology just because it is a college course.