In order to prepare for an interview and help you feel less anxious about the experience, it's helpful to spend some time thinking about how you would respond to certain questions. To start, consider some of the skills that would be important for the position for which you are interviewing. For example, if you are interviewing for a marketing position, some important skills for the job would be an ability to communicate effectively, project management skills, teamwork, and maybe creativity. With these skills in mind, think about previous work experiences and/or classroom experiences you've had where you demonstrated these skills. (Experiences with a campus or community organization are acceptable too). Maybe you demonstrated communication skills through the many presentations you were required to give as a part of your coursework, and maybe your professor asked you to speak at a campus-wide event because she was so impressed with your speaking abilities. An example of your project management skills might be the time your boss at the restaurant asked you to evaluate the possibility of bringing in live music on weekends. You had to consider the costs, the revenue, the space required, the audience it would attract, the competition in the community, etc. and make a recommendation based on what you learned. Many times, we don't realize the skills we are developing on the job and in the classroom. Don't sell yourself short when you think about your skills and abilities. Chances are, you've accomplished more than you think you have.
It may be helpful for you to write down some of these examples to help clarify them in your mind. You don't want to memorize responses to the potential interview questions (you want your responses to be natural), but you will likely feel more comfortable going in to the interview if you've considered how you may respond to some of the questions.
If you are about to graduate or have recently graduated, you should also be prepared to speak to your interest in this particular career, what classes you felt benefited you the most and why, what coursework you enjoyed most/least, campus activities, etc. All candidates should be prepared to speak to why they want the job, why they are interested in the organization, how their knowledge and skills will contribute to the organization, successes/failures, and why the organization should hire them.