Complete your seminars and coursework quickly. Most graduate schools will limit the number of hours you can take each semester; taking the maximum number of credit hours (plus summer school and winter session courses when they are offered) can be an effective way to knock out the required course credits quickly.
Maintain a work-life balance throughout your doctoral program. Some students fail to finish because they get burned out on coursework and reading. Following a regular exercise routine throughout the week can give you the energy you need to get through long hours of reading and studying. Exercising early in the day before you get started on your studies is an effective way to ensure that you exercise each day and that you invigorate your body for the rest of the day.
Teach a course at a local community college or online. While, on the surface, this may seem counter-productive, it can be an effective way to solidify your own knowledge of the field for your comprehensive exams. You may be completing some of this work already if you obtain an assistantship. If not, you can obtain a part-time teaching position once you have earned enough credits to qualify for a master's degree.
Budget your time and the required reading list. Many Ph.D. programs in the arts and sciences require a working knowledge of the top scholarship in the field on various topics within your discipline. There is usually a required reading list that you will be expected to complete and will then be tested over during your comprehensive exams. If you calculate the number of weeks you have until you plan to take your exams and divide that number into the number of books or articles you are expected to know, you will know exactly how much reading you should do each week. Stay on schedule.
Research your dissertation topic from day one. Even if the topic changes slightly or completely, you should continue conducting research from the outset of your studies. You do not want to wait until your coursework is nearly over to begin this process. Having everything started and nearly done by the time you reach your comprehensive exams will give you the boost you need to finish in a reasonable amount of time.