The main problem that I see that people have are lack of critical thinking skills. A lot of those who are failing are the younger kids with the minimum requirements to get into the program. Those who have the A's have a minimum bachelors degree and have been actively continuing their education while waiting to get into a nursing program. e.g. taking Developmental Psychology, Pharmacology, Pathophysiology, Sociology, Argumentation, Philosophy, and Logic.
If you can and have time and would like to be ahead before even entering a program, I suggest you pick up some Nursing Process books. Our school uses the Roy Adaptation Model. Some schools use other theorists.
If you would like a sample of the first semester module of my school, send me a PM. It'll give you insight about what's expected of you and just how tough it is.
edit: Try and take a medical math
or dimensional analysis math class. you don't want to fail out of your nursing program because you can't pass a simple math test.