Your CV may be impeccable, and your qualifications may make you a perfect fit, but that doesn't mean you won't be turned down for a job. Sometimes that will happen for no reason -- but in some cases, it's likely your fault.

That may sound harsh, but it's important to take a hard look at why you may be getting passed over. Only then can you work on improving your odds of getting hired.

Remember that the supervisors making hiring decisions are often conservative. They may be looking for a reason to not to hire you, because making a mistake may be worse for them than hiring a mediocre employee.

The good news is that some mistakes are easily avoided. With a little work, you can make sure you don't set off any red flags and get the job you deserve.

Young people sit in a row using a variety of devices.

Make sure your social media is in order before applying for jobs. Image source: Getty Images.

1. Your social media presence is unproffesional

If you're being interviewed for a job, chances are someone in human resources (HR) will do an online search for you. In fact, 70% of employers are using social media to screen candidates, according to a 2017 CareerBuilder report.

While there are no definitive rules as to what an HR person might be looking for, there are some obvious red flags. Make sure your social media presence is professional. It's OK to have a photo from a wedding where you're involved in a champagne toast. That picture of you doing a keg stand with no shirt on may not reflect well on you.

In addition, make sure your social media presence is largely benign, and understand that expressing your political, religious, or other personal views may lead some employers to turn you down. That may not be fair (or even legal), but it's a reality.

2. You have no social media presence at all

"Most workers have some sort of online presence today -- and more than half of employers won't hire those without one," says CareerBuilder chief human resources officer Rosemary Haefner. "This shows the importance of cultivating a positive online persona. Job seekers should make their professional profiles visible online and ensure any information that could negatively impact their job search is made private or removed."

That does not mean you should have a profile on every service, but you should at least have a well-developed LinkedIn presence. It's also not a bad idea to be on Facebook, even if all you do is follow family members and close friends while making the occasional inoffensive post.

3. You stretch the truth

Social media and the internet have made it easier for potential employers to fact-check your resume. Exaggerating your work responsibilities or taking a little too much credit for a project or an award could come back to haunt you. It's best to be honest and make sure your resume reflects your actual accomplishments.

4. You fail the politeness check

Sometimes, especially in a competitive hiring situation, the little things matter. If you're basically tied with another candidate for a position, then a small mistake may tip the scales against you.

One little error that many job applicants make is failing to send a thank you note after an interview. That may seem small, but it's easy to do, and it's a basic show of politeness. Whether through email or snail mail, send your interviewer(s) a brief note thanking them for their time and consideration. Not only will it show gratitude, but it will give you a chance to drive home any points you made (or failed to make) during the interview.

Be thorough

Think of the job application process as a competition and look for every edge you can get. Some of the missteps above may not matter to a specific HR person, but to another they may be absolute dealbreakers. It's always better to put in too much effort and do a few things that don't matter than to miss something that keeps you from getting the job.

Daniel B. Kline owns shares of Facebook. The Motley Fool owns shares of and recommends Facebook. The Motley Fool has a disclosure policy.