Although many nurses use math in their jobs, advanced math skills may have taken a backseat to more practical skills. To excel in a Ph.D. program, you'll need to be able to quickly analyze data and make recommendations based on numbers. This means you'll need a strong background in algebra and calculus and a general familiarity with probability and statistics. Depending upon the nursing program in which you enroll, you may be required to take these classes or others that build upon a framework of basic calculus and statistics.
Nursing is a science, and you'll need a strong background in life and physical sciences to do well in a Ph.D. program. Courses in physics, chemistry, biology and physiology prior to graduate school provide the core knowledge you'll need. The answers to problems you'll face as a nurse aren't always readily apparent, and you'll need to know how to intelligently question scientific research and unsupported claims. Thus, you should take classes that develop scientific and critical thinking.
You'll need strong research skills to excel in a nursing program, particularly if you're pursuing a research-oriented nursing degree. This not only requires a strong background in math and science, but also the ability to seek out good sources, to conduct full reviews of existing literature and to formulate your own well-designed research projects. You'll likely be required to draft a dissertation, and this demands sufficient creativity to pursue a novel research topic, as well as the expertise needed to defend your ideas.
Nursing programs can be highly demanding. You may have to balance the time you devote to your classes with the time needed to complete internships, independent research projects and dissertation writing. Poor planning skills are just as likely to cause bad grades as lack of study. Time management also means balancing your personal and academic lives. If you're working and going to school, you may need to transition to part-time work, and if you have children, you might need extra help with childcare or additional support from your partner.