The best tips I've been given and that I have used on interviews:
If you don't have an answer at that moment, ask for a little bit of time to think about it, or if it is possible to come back at that question later in the interview.
It is ok to bring a notebook with some answers prepared.
Dress for the job you want.
Always have at least one question to ask them at the end of the interview (or when prompted)
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The best tips I've been given and that I have used on interviews: