Probably a bit late to help you today, but some thoughts. Numerous companies now use behavior interview technique. Instead of asking questions about you, why you are qualified, why you deserve the job, etc., you will be asked to give examples of how you handled actual situations previously. For example, you might be asked "Tell me about a time you had to persuade a co-worker." or "Tell me about a time you had too much to do. How did you prioritize what you would accomplish." The interviewer is looking for you to describe the situation, the tasks involved, actions you took and the results of your actions.
The competency interview is similar, as it asks about a situation. The interviewer then follows with questions about how you did it, why you did what you did, what did you learn and how has it helped you.
I have seen these types of interviews catch the interviewee off-guard. To prepare, it helps to list some experiences to draw upon and try to answer some sample questions to yourself. They don't have to be about how you saved the company from certain destruction, just examples of how you effectively dealt with a situation using a logical, efficient and effective methodology. Search online for "behavioral interview" or "competency interview" for examples.