"I interview prospective applicants at job fairs. I try to break up the interviews and allow a little recovery time between them, but often my schedule is packed solid. What can I do to make sure that my assessments of the candidates are accurate and not influenced by order effects?"

You've already taken the first step—just recognizing that order effects can occur will put you on your guard and make you less susceptible to them. Another precaution is to avoid making a final decision during the interview itself. In stead, take notes about an applicants' strengths and weaknesses, using concrete examples that will help to jog your memory later. Then, at the end of the day, review your notes and make decisions in the context of the entire applicant pool.