Take the GRE general and subject tests. These standardized tests are required by most graduate English programs throughout the United States.
Research your area of focus and begin to put together an idea of what subject you would like to do for your dissertation. Many programs are anxious to hear about your research ideas with your application.
Craft an exceptional letter of interest to accompany your application packet. Program administrators are looking for an enthusiastic commitment to the discipline of English and appropriate research.
Strive to make your class papers publishable. By the time you are active in a PhD program you're expected to strive towards a high degree of professional development that will bring credit to your school.
Attend academic conferences regularly in order to understand the contemporary conversation about various discipline specific issues. Your school can often help you with the cost of attending many of these English PhD events.
Work consistently on finishing your PhD dissertation. Many PhD students work through the classes only to leave the last major project incomplete, greatly devaluing their education.