There is really an art to answering those questions. Knowing the content and what the diseases are... is not enough to pass the exams. Nursing students need to learn how to think critically. That is... once you know the "what is", you need to know "why" something is happening and "what" should the nurse do given a certain situation.
Practicing NCLEX type questions after studying the material will help you expand on how to think and connect loose dots. There are several books that help you develop this skill by giving you tools on how to approach the questions. I would ask your professor or librarian for suggestions. In my case, I use Kaplan's "NCLEX-RN Strategies for the Registered Nursing Licensing Exam" book... but there are other companies that prepare the same type of books. Go with the company your school uses for testing. My school uses Kaplan University's materials, so I stick to Kaplan products.
The key to success is practicing those NCLEX type questions
, over and over.
Hope this helps!