how do i boost my confident in an interview with a very tought companies?

Straight forward and properly arranged for the interview

Just be yourself and make sure that all your answers are as accurate as possible.
If you don't know the answer to a particular question, do NOT try to come up with something silly, just tell the interviewer that you don't know.
All keep in mind that the person interviewing will ask you questions to which he knows the answers and giving them the wrong answer will just create a bad impression.
Keep eye contact at all times, make sure that when shaking their hand, your grip is firm.

Just be yourself..Put your best foot forward and sell yourself but then again you should back it up with outstanding performance when hired.