As a rule, all the Universities for admission accept the results of the exam, and at least partially passing score is made up of these markers. To retake the exam in the same year is impossible. So, hoping for a successful job interview, you should not forget about the successful completion of other exams. Moreover, interviews with applicants, and usually are the final part of entrance examinations.
Even passing all the exams with "excellent", you can't be sure of their enrollment, as the interview is not yet completed. It may significantly lower the total score, but may, conversely, bring in you in the first rows. Sometimes, school honors "swamped" interview, because it involves skills not particularly developing in ordinary schools: communication skills, lateral thinking, the ability to quickly "grab" situation.
Before the interview, take the time to find the students chosen specialty, who passed examinations up to you (preferably the year before). Ask them to think of questions, conversation, anything. The topics of the interview can be arranged at the University in advance. Meditate on these topics, read what they write about it in the news, in the current research. The examiners here will be important not so much knowledge (you showed them in writing) how your interest in the specialty, do you follow the latest developments in it, do it yourself study.
And, of course, there are General guidelines that will help you to interview not only the University, but also, for example, when applying for work.
Stand straight, be confident (but not cocky). Look into the eyes of the examiner, but not aggressive and are friendly. Smile. Watch his speech: it should be smooth, the voice is confident, not trembling. Do not try to answer questions immediately, take some time to think, this is perfectly normal. Do not attempt to change the subject, if you do not know the exact answer. Try to solve the problem logically. And don't try to convince the Commission that in fact you - a connoisseur of this region. It is possible only to mention in passing something that interests you; maybe you yourself were engaged in the study of any question in your specialty, unobtrusively inform.