Don't overprepare: That's right. Don't overprepare. Naturally, you want to be prepared, but you don't want to sound like you've memorized a speech. Think about how you might answer common interview questions, but actually listen to what the interviewer is saying. Repeat it back to them if necessary (and to buy yourself time).
Be a little casual: I'm not talking about wearing jorts to the meeting. But don't be afraid to speak in a more casual manner. Talk like yourself, not like a book you read about interviews. If you want to practice your extemporaneous speaking skills, ask a friend to give you different questions and prompts so you get the hang of answering quickly, but honestly.
Have your own questions ready: Yes, we know this isn't necessarily public-speaking related, but having 3 or more go-to questions ready will help immeasurably in keeping up the flow of conversation between you and the interviewer. It can also give you a chance to cover any of your skills and experiences that haven't already come up.
Good luck! The job market is tough, but never forget - you're interviewing THEM too.
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