The interview is your opportunity to showcase your product (YOU). This is where you have the opportunity to "wow" the interviewer and sell yourself. The resume got you in the door but the interview is what secures the job. So, given that the interview is where you seal the deal, you must present yourself in the best possible light and distinguish yourself from the competition.
Recruiters, interviewers and hiring managers critique you in every aspect of the interview including your diction and grammar. Check out this article from Monster.com (http://bit.ly/Ry4a2). It gives "Six Sloppy Speech Habits."
What I've noticed in my years of recruiting is that oftentimes a candidate becomes comfortable in an interview and lets their guard down and becomes so relaxed that they begin to talk as if they were out at a picnic among friends. I start to hear slang "ain't, gonna, my bad" etc. This is not acceptable to an interviewer no matter how comfortable you are with him/her.
In the article link above, numbers 1 and 4 really resonate with me as I hear them oh so often. We all use "um" especially when nervous. I recommend that if you are preparing for an interview that you prepare a short story about yourself and leave it on your voicemail and then play it back and count the "ums." You'll be surprised.
Last but not least, be cognizant of pronouncing "with" as "wif" or pronouncing words such as four, store, walking, running, talking (fo, sto, walkin, runnin, talkin). In an interview you are evaluated on everything so put your best foot (or speech) forward, sell yourself and get the job!
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