Complete an undergraduate degree in a broad field

To qualify for a PhD program, you will need a solid record of undergraduate coursework from a reputable university. This degree should demonstrate your potential for both advanced coursework and independent research. In general, you need to maintain a high GPA and develop a good working relationship with your instructors.
Generally, its recommended that students interested in pursuing advanced degrees should develop a wide skillbase during their undergrad. In other words, while you may ultimately be interested in studying Zoology, an undergrad degree in basic Biology might provide you with a diverse base that youll be able to narrow in your future studies.
Many universities offer majors designed to funnel you into an advanced degree. Prelaw majors and Premed majors are two notable examples of this. Talk to your academic advisor about your interest in pursuing a PhD after you graduate, if youve yet to select a major.