being invited to the interview is the first big step in the admission process. first of all, relax and be yourself.... be confident but not overconfident. every experience is different but i am going to tell you about mine.... there many posts on this site that would give you an idea of what questions the interview panel may ask to candidates...
three people did my interview at drexel ( program director, assistant director, and faculty professor). everybody was very nice..... the actual interview lasts from 30-40 minutes. they will ask you clinical and personal questions which involve acls protocols, acute chest pain, analgesics, vasopressors, post surgical patients (blood loss, fluids), and hemodynamics. personal questions such as strengths, major weakness, family support, why you want to be an crna, role of the crna, and your icu experience sickest patient and worst shift. sell yourself and show them why they should pick you over the rest of the applicants ( your experience, your attitude, your hard work, certifications...) if you can not answer the questions... do not panic... be honest and do not try to bs them. of course, do not forget the basics of an interview (arrive early, attire, attitude..)
again, relax, be yourself, and pray... you will do great.... good luck