They meet more people in an afternoon than most of us do in a year. But what faux pas do human resources pros see again and again during the interview process?

We picked the brains of two high-profile executives to find out what you definitely should and shouldn’t say, as well as what they secretly think of your résumé.

Not Knowing When to Stop Talking

“Talking over your interviewer is the biggest mistake that interview candidates don’t realise they’re making,” says Stacey Hawley, a career and leadership development coach and compensation specialist. “This is usually from nervousness, but, as a result, the candidates outtalk the interviewer and don’t engage in active listening.”

Amy Michaels, a human resources director at a high-tech firm in New York City, agrees: “The inability to listen is huge. That person who’s always trying to have the exact right answer but can’t stop talking? They ultimately won’t be a success.” Instead, listen up and watch more subtle clues — like your interviewer’s body language. If she’s shifting back and forth or clearing her throat, it’s time to let her get to the next question.

Bad-Mouthing Your Ex-Job

While it may seem like a no-brainer, putting down your current employer happens all too often, says Michaels, perhaps because the bad feelings are still fresh. If you’re tempted to trash your present company, stop right there.

“When I ask why you’re leaving a place, I don’t want to hear you gripe about your current manager or badmouth your situation,” she says. “Be creative enough to come up with a tactful reason as to why you’re leaving. Otherwise, to me, that’s a huge red flag that you’re not mature enough to know not to do it. Not to mention that it makes me nervous about how tactful you’re going to be externally if I hire you.”

Not Acknowledging Your Mistakes

A couple of interview rules of thumb: “Be well-groomed, and be on time,” says Michaels. “Or email if your train is running late. That happens in New York.”

While one minor transgression may not deep-six your prospects of landing the job, you should still acknowledge it and move on, says Michaels. Hawley will also pardon small errors: “Mistakes are OK and acceptable. No one is perfect — or needs to be.” The bigger red flag, both say, is someone who can’t admit their missteps. “The people who make me nuts just act like being late never happened,” says Michaels. “If you make a mistake, own up to it.”

Neglecting Your Cover Letter

Our experts were adamant about this. “To be honest, I don’t read objectives, and I don’t care if you fence,” says Michaels. “But I do read cover letters.” Hawley agrees: “Absolutely write a cover letter. It’s an opportunity to highlight your understanding of the business, and what you can do for the bottom line.”

And, even in the digital age, there’s no excuse for a quickly dashed-off email — take the time to compose it with care. “Demonstrate your knowledge of the company,” says Hawley. “And link your past achievements to the position, showing how you can contribute to their future success.” That, she says, will always make a candidate stand out.

Trying Too Hard

While confidence is a must, check your supersize ego at the door. “I have a good radar,” says Michaels, “and I have a policy where I will not bring in ego. I’ve made that mistake, and it really affects the culture of an organisation.”

What good HR professionals have that most humans don’t, notes Michaels, is a high EQ. “You notice body language,” she says. “You can sense whether someone has empathy or is overly self-involved.”

Michaels advice? Try to relax and be your (best) self. “I like people who are authentic, and you know it’s who they are,” she says. “I’m just attracted to that.” Of course, HR execs can also pick up on whether you’re posturing. “When you start elaborating on things you don’t actually know or things you think I want to hear, I’m not impressed,” she says.

Curbing Your Enthusiasm

If you’re going to the trouble of sprucing up your résumé and dry-cleaning your suit, at least try to appear appropriately enthused. An interview is an opportunity to learn about the company and vice versa, but you can take yourself out of the running prematurely if you don’t act like you want the position. And that includes doing your homework on both the company and your individual interviewers.

“I would never hire someone who didn’t do the proper research,” says Hawley. But if it came down to a choice between two candidates, “all else being equal, the person who showed the most excitement and interest would get my vote,” she says.

Forgetting Your Manners

When it comes to an interview, you want to dot your I’s, cross your T’s and, yes, put your résumé on nice, thick paper stock — but certain old-fashioned politesse can also get you ahead.

“A handshake is actually important to me,” says Michaels. “It’s a totally stupid thing, but I do pay attention.” So what is she looking for? “You want a firm, confident handshake,” she says. “It tells you whether that person is an introvert or an extrovert. If it’s a sales job, you have to have a healthy handshake.”

As for Hawley, her biggest interview-etiquette pet peeve is equally simple: not following up. So be sure to send a thank-you note or a thank-you email, if you’re trying to be expedient. But don’t just send a form letter to every person who you interviewed with — thank them instead by mentioning a personal connection or a particular detail that you discussed.

This article was an excerpt. Read more: HR Experts Confess: 8 Biggest Job Interview Mistakes We See [via LearnVest]