The Equal Employment Opportunity Commission (EEOC) has guidelines you can download here.
Here is just a sampling of areas where you need to tread lightly—or steer clear of.
Age/Race/Color—You are permitted to ask if the candidate is 18 or older and if they can supply proof of age if hired. You cannot ask questions that are aimed at finding out if the candidate is over 40. Any questions that directly or indirectly relate to race or color are illegal.
Physical Health—While you may not ask general questions that could lead to the candidate identifying health conditions that would not reasonably relate to the job, you may ask specific questions as long as they are directly related. For example, if the position requires the individual to lift 40 lbs. regularly, you may ask if anything would prevent the candidate from lifting 40 lbs.
Residence—You cannot legally ask if the candidate owns or rents a home. You are permitted to ask for an address for contact purposes, or if it will be a problem to get to work at a certain time.
Family—It is illegal to ask a candidate about marital status, about a spouse or spouse's employment, child care arrangements, or dependents. You are permitted to ask about a work schedule, including "Can you work overtime?" (for non-exempt employees).
In addition to these topics, the Fair Inquiry Guidelines outline lawful and unlawful questions relating to relatives, pregnancy, name, sex, photographs, education, citizenship, national origin and ancestry, religion, military service, height and weight, and arrests and convictions. Review them before you interview and you will help protect your school from potential lawsuits.
For a more in-depth resource on hiring practices, check out ISM's Safe and Effective Faculty Recruitment, Retention, and Dismissal Practices in our Bookstore.