Sincerity is discernible and insincerity is unmistakable. Since a graduate program means extensive work with one or two faculty members, you would be wise to research the faculty in your area of interest. Know who they are, research what they have written, and read what they have written. In your statement of purpose, if you can say you are interested in studying a specific area, explain why and then go on to elaborate your familiarity with the work done by faculty member X in this area. Committee members will see that you have done your homework.
Some schools require an interview for acceptance.
If you are applying for an assistantship or fellowship, an interview may also be required. If the school does not require an interview, it would still be advantageous to schedule a time to meet with a faculty member or chairperson of the department for which you are applying. This meeting provides an opportunity to obtain more information about their school and the graduate program. Before the interview, you should read over the catalogue to become familiar with the institution's goals and functions. Tell me about your experiences in your field of interest.