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CNBC managing editor reveals the 11 most common job interview mistakes

In previous jobs, and now in my role as a managing editor at CNBC, I've conducted dozens of job interviews.

I've seen the good, the bad and the ugly, and I'm consistently amazed at the very basic things that candidates screw up.

Here are the most common interview mistakes I see people make.

1. Arriving late
Since job candidates often have several interviews with different managers scheduled back to back, two things could happen when you show up late: Either your first interview is cut short, or you disrupt the schedules of several interviewers. Neither is good for you, since it either shortchanges your time with an interviewer or makes multiple people grumpy.

2. Arriving too early
On the flip side, arriving too early can also irritate a hiring manager, since it is equally disruptive to their schedule. It's important to arrive at least 10 minutes early to get through any security and check in with reception, but it's a mistake to arrive any earlier than 15 minutes before your scheduled interview time.

3. Appearing unpolished
Looking put together signals that you care about the interview and want to put your best foot forward. However, all too often people show up to interviews appearing rumpled, wrinkled, stained and wearing clothes that don't quite fit. It's not a fashion show, but it is important to carefully select your outfit, brush your hair and take a look in the mirror before you arrive.

In the movie "The Internship," adult Google interns make every mistake in the book.
Source: 20th Century Fox
In the movie "The Internship," adult Google interns make every mistake in the book.

4. Not bringing a resume
In an ideal scenario, the hiring manager would be ready with your resume, but days are busy and not every interviewer is organized. That means you should always have a copy for each person you expect to meet with, plus some extras in case you have unexpected interviews. Not only is it practically helpful, it signals that you are thoughtful and prepared.

5. Displaying low energy
This one is hard to define but an interview killer. Here's what it looks like: Slumped shoulders, lack of eye contact, slowness to respond to questions, and a general lack of enthusiasm for the company or role. If you don't clearly want the job, it's near impossible to persuade someone to give it to you.

6. Focusing too much on themselves
Talking endlessly about what you want, how this job is the direction you want to go in your career, and how the experience would be great for you is meaningless drivel to an interviewer.

Companies don't pay you to help you out! They hire you because you have traits and skills that will help them achieve their goals. Use your responses to illustrate how you can be of service to the hiring manager.

7. Seeming unprepared
Further, not demonstrating a basic knowledge of the role or providing clear examples of your past performance makes it seem like you just rolled in after only glancing at the company's website.

Interviewers tend to ask the same fundamental questions about your background, skills, interest in the company and why you think it's a good fit. At minimum, read up on the company and prepare a few anecdotes about projects you successfully completed.

In "Gilmore Girls: A Year in the Life," Rory Gilmore bombs an interview after showing up unprepared.
Source: Saeed Adyani | Netflix
In "Gilmore Girls: A Year in the Life," Rory Gilmore bombs an interview after showing up unprepared.

8. Not having any questions
Most interviewers leave time at the end to answer questions. Usually, they know you're vetting them, too, and want to make sure it's a two-sided conversation. It's also a bit of a test. The questions you ask often reveal the way you think and what's important to you. It also shows that you care enough about the job that you want to know more.

Not having any questions prepared signals you don't care, aren't curious, or haven't done your homework. If you freeze up, throw out an old standby question like, "What does success look like in this role?" or "What's the culture like here?"

9. Asking weirdly personal questions
Conversely, some candidates get a little too personal with their questions. I've had people ask me about my family, previous companies I worked for and why I chose to leave one company for another. This line of questioning might make the hiring manager feel uncomfortable and also doesn't illuminate anything for you or them.

10. Forgetting to follow up
So many people forget this basic rule of interviewing: Follow up within 24 hours by email to thank the interviewer for their time and underscore your interest in the position. If you don't do it, hiring managers may think you're not interested or organized, or they may simply forget about you.

11. Following up too aggressively
While it's important to follow up, you should not send multiple emails or call an interviewer. It is extremely awkward to receive a call out of the blue from someone demanding to know why they haven't heard from you. Send your follow-up email, and then move on with your life. Anything more is probably too much.

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