Decide what your primary research focus is going to be before applying to any economics programs. A Ph.D. is a research degree, and you will be expected to make a contribution with your scholarship in the field as you develop and write your doctoral dissertation. Knowing what area of economics you are going to research prior to enrolling or even applying to a school can speed up the process of completing your doctorate quickly.
Read extensively in the sub-field of economics you will specialize in, and learn who the major scholars are in that field. Conduct research to determine if those scholars are still teaching at any major universities. (Some may have retired or taken jobs in the financial sector.) Contact the scholars who appear to be the leaders in their field. Discuss your research interests and determine whether or not they might have an interest working with you, if you are able to get into their school's doctoral program. Ask them for a reading list and any direction they might be able to provide regarding your doctoral dissertation research.
Conduct your reading and research prior to applying for schools. You can utilize the fact you have spoken with other scholars in the field and have already begun to conduct research as a way to better promote your doctoral application to various schools. Schools with scholars who have research interests that match yours will be more likely to consider your application.
Submit your application to programs that line up with your research interests. Apply to some of the top schools in the nation as well, if they are not included in your list of potential schools. In most cases, the top scholars in the various sub-fields of economics will be found at the top schools anyway. Top-rated schools often focus on producing top Ph.D. graduates and will often let you into a Ph.D. program without requiring you to obtain a master's degree first. Some of the top schools in economics at the graduate level include Harvard, the Massachusetts Institute of Technology (MIT), Princeton, the University of California-Berkeley, Yale, Northwestern University, the University of Pennsylvania and Columbia University. These schools comprised the top-10 schools in economics, as ranked by "U.S. News & World Report" in 2009.
Complete your coursework during the first 2 years of study in your Ph.D. program. Depending upon the requirements of your school's economics department, you may need to take summer courses to get this done in just 2 years. By making this your goal, you will then leave the remaining 3 years to complete your comprehensive examinations and your dissertation. Ideally, you can study for 1 year in preparation for your exams while working on your dissertation. The final 2 years can be devoted to completing your dissertation.