The No. 1 interview mistake job candidates make is surprisingly simple

Aubrey Plaza as April Ludgate, Amy Poehler as Leslie Knope on NBC's 'Parks and Recreation.'
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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 constantly amazed at the basic things that candidates screw up.

The No. 1 thing that can ruin your job interview is surprisingly simple: Displaying low energy.

I've seen it plenty of times myself and have heard it from many different hiring managers. While it can be hard to define what exactly "low energy" means, here's what it typically looks like:

  • Slumped shoulders
  • Lack of eye contact
  • Slowness to respond to questions
  • Not smiling
  • Flat speaking voice
  • Leaning back in the chair
  • Not asking questions
  • A general lack of enthusiasm

It comes down to a simple truth: If you don't clearly want the job, it's near impossible to persuade someone to give it to you.

Kate White, the former editor-in-chief of Cosmopolitan, underscores this point in her career advice book "I Shouldn't Be Telling You This." After years of analyzing why some candidates dazzled and others disappointed, she realized the ones she liked seemed excited to be there.

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"There's even a little bounce to their step when they walk into the room, and you may sense that bounce even when they're sitting in the chair talking to you," she writes. "They want the job, and they're not afraid to show their passion."

White says too many people tamp down their enthusiasm because they're nervous or worried about seeming unprofessional, and it's the worst mistake you can make. "Here's what you must remember: It's the hot tamale who wins the day, not the [candidate] who's as cool as a cucumber," she says.

What can you do to make sure the interviewer sees how much you care? Start by smiling wide and sitting on the edge of your seat with your feet firmly planted on the ground. Come prepared to talk about why you're a great fit and what you've achieved in the past. Ask lots of follow-up questions.

Energy is contagious. If you show that you're excited about the job, the hiring manager is much more likely to be excited about you.

See also: The 11 most common job interview mistakes

And don't miss: Marcus Lemonis reveals the one question job candidates should never ask in an interview.

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