Enroll in the right Masters program. A Master of Arts (M.A.) is the best degree to get if you want to pursue a Ph.D. in creative writing. A Master of Fine Arts (M.F.A.) in creative writing is considered a terminal degree and generally doesn't have a strong academic focus. An M.A. in creative writing generally has an academic as well as creative focus, and leads naturally into a Ph.D. program.
Decide why you want a Ph.D. in creative writing. A Ph.D. can help you get a tenure-track professorship in today's tight market in creative writing. Beyond that, a Ph.D. program gives you time to formally study your field. If you just want to write, it's better to get an M.F.A.
Research which universities offer a Ph.D. in creative writing. Until recently, very few universities offered anything beyond an M.F.A. or M.A. in creative writing, but the rising number of graduate students in creative writing has led to an expansion of creative writing programs.
Be prepared to research for your Ph.D. in creative writing. Qualifications for the dissertation vary from school to school, but most schools require a research/analysis component. If you have little or no interest in analytic writing or research, reconsider your decision to get a Ph.D.