1,Never fake yourself and if you plan to do it,rehease a 1000 times and do,else dont do it at all.
2.Never cut the eye to eye contact with the interviewer.Not only your words but your eyes are also speaking volumes.
3.Never come unprepared,incase you couldnt make it,rehearse and always deviate the attention of the interviewer to a topic that you know well.
4.Never come in bright ,revealing outfits because the old men present in most of the interviews wont like it.
5.Never lose you C and C (Confidence and Composure).Even if you lost one,half is lost.
6.Never make a "Kind of" or "something like that" or "i think" kind of answers.If you dont know it,just admit it and dont beat around the bush.Most of them will screw you big time .
7.Never ever overboast about yourself,cos they dont care a damn and again they will get freaked out if you do that.
8.Never try to answer the questions of more than one interviewer at a time.Just tell the next guy a few seconds.
9.Dont place unwanted and artificial mannerisms when you talk.
10.Last but not the least ,never ever change you accent or your way of speech which can ruin everything that you acheived 5 minutes back.