Depending upon which background the interviewer is from, he/she will generally test very basic technical knowledge and communication skills. If the questions seem too hard, remember its their way to check if you succumb under pressure or not. Prepare for conceptual questions form the subjects which are considered to be the building blocks of your field of study. Keep the smile on your face as much as possible and reply in a firm, confident tone. Also, a firm hand-shake at the end of the interview is the right gesture to put forward.