What are some of the things you have learned not to do when you are interviewing for a job?

couple weeks ago and also last year I had 2 interviews where I thought of myself to be an excellent fit for the role but hirers didn't think so so I'm betting on discrimination although I possibly did a couple things wrong and I don't think I can afford myself to keep doing those mistakes. I heard somewhere that a prepared man worths twice so let your experience rain