Source: This article was originally published on CNBC.

Written by: Courtney Connley, CNBC Make It

Employers will try to get beyond the standard Q&A by using all sorts of ‘techniques,’  in order to see if you’re the perfect candidate. 

Regardless of how qualified you are for a job, saying or doing the wrong thing in a job interview can easily hurt your chances.

There are three things you should make sure to do before, during and after an job interview — as well as one mistake you should make absolutely sure to avoid:

1. Dress appropriately for the environment 

While a suit and tie or high heels and a skirt may no longer be the traditional interview uniform, that doesn’t mean you can totally relax your attire.

Ask someone you know about the dress code at the company or doing a simple Google search to find images of current employees. Then, you should pick out an appropriate outfit for the occasion that’s comfortable, but not too flashy.

At the end of the day, and interview, you want people talking about your ideas after you leave, not your outfit. Keep that front of mind, and you’ll look just fine.

2. Be direct: Say you want the job

After you’ve discussed your background and accomplishments, you should end the meeting by telling the employer one thing: “I really want this job.”

Doing this, won’t make you sound desperate. It will show hiring managers your sincerity, courage and humility. The person hearing it knows it’s difficult to say, they know it takes moxie, and they’ll remember that.

In the end, you must remember that your goal in an interview is to make your case”and give it your all.

3. Follow up promptly

Performing well during the interview is only half the battle. It’s what you do after an interview that can make or break your chances of getting an offer.

In addition to writing a personalized thank-you note that expands on at least one point of discussion from the interview, you should edit your social media accounts and connect with your interviewer on LinkedIn.

After your interview, post intelligent tweets about your industry or the economy, and please, avoid stupid Instagram pics. That when sending a LinkedIn request you don’t want to just click a button. Instead, say something about how much you enjoyed meeting and discussing x, y or z.

And one mistake to make sure you avoid

Acting too casual or relaxed during a job interview is one of the biggest blunders you can make.

There was a time when I made this error as a recent Harvard University graduate who was interviewing for a reporting job with the Kansas City Times.

While riding to lunch with a group of editors from the paper I remember asking, “So, what kinda food we getting?” as if they were old friends. I recall meeting with the editor-in-chief later that day and asking him where he lived, as if I was scouting local real estate.

The next morning I got a call letting me know that I didn’t get the job because I didn’t “fit in.” The editor didn’t have to explain himself, I was dumb, but not so dumb that I didn’t know I had overstepped.

Even if you think you’re perfect for the job, you need to always remember, they are the buyer, you are the seller.

Do not, let down your guard.

Suzy Welch is the co-founder of the Jack Welch Management Institute and a noted business journalist, TV commentator, and public speaker. Through its online MBA program, the Jack Welch Management Institute transforms the lives of its students by providing them with the tools to become better leaders, build great teams, and help their organizations win.