You need to be familiar with topics that are not permissible as interview questions to avoid possible discrimination lawsuits. Examples would be race, ethnicity, gender, religion, age, health, illness, disabilities, and national origin. Stay away from all questions and conversation that is not related to the job unless they are just some nice pleasantries like hobbies or the weather. Absolutely refrain from making any illegal type of statements or asking discriminatory questions. Go to this link to help find out what are considered illegal questions to ask during an interview: http://www.eeoc.gov/.
***It is a good idea to have at least two people responsible for interviewing and hiring applicants. Not only will you get a second opinion, it can help support the decision not to hire if the unsuccessful applicant files a discrimination charge.