Everyone knows preparation, eye contact and being punctual are key during a job interview — but it turns out what you wear on the big day could also be crucial.

And according to one expert, there's a surprisingly common fashion faux pas many jobseekers are making regularly without even realising it.

Pamela Jabbour, the founder and CEO of workplace uniform company Total Image Group, told news.com.au many people overlooked the importance of appearance during the job application process.

"In general, what you wear is a reflection of who you are and a lot of first impressions are based on the visual, even before the person speaks," she said.

"That follows through into interviews — you are competing with a whole lot of other people for the role and you only have a short window of 45 minutes to an hour to sell who you are. "It's hard to really get a vibe about someone in that short time, but what you're wearing solidifies that."

Jabbour said candidates should dress to reflect the status of the position they are applying for, as well as the culture of that particular workplace.

She said jobseekers should always ask about the company's dress code before the interview, and that people who hoped to land a high-ranking position such as chief financial officer were expected to dress more formally in a suit, while "smart casual" was the best option for most candidates.

"For guys it's really easy — chinos or business pants with a buttoned shirt is always a safe way to go, depending on how formal or how senior the position is," she said.

"Anyone working in finance needs to dress with a level of seriousness while those in marketing for example have an element of creativity, so they can wear smart pants without a tie or a skirt with a blouse — knee-length skirts are always safe.

"If you dress up a bit it does no harm, while a lot of harm can come from being underdressed."

According to Jabbour, there are several big no-no's when it comes to dressing for an interview — including one popular footwear choice.

Apparently, open-toed shoes — no matter how conservative or high quality — should never be worn as they can make the jobseeker seem unprofessional.

"Open-toed shoes for girls or any form of sandal or thong is a bad idea," she said.

"In terms of clothing, anything too revealing such as low tops in the front or the back are out. "So are jeans and T-shirts, and anything sparkly or overbright with a pattern that detracts from you as a person.

"My pet peeve is overexposed undergarments, because it's really distracting to try and stay serious when someone's lacy bra is poking out — it's not a good look."

Ms Jabbour said candidates should steer clear from bright colours or loud prints and instead opt for understated items in colours like navy, charcoal or black and white.

She said while heels weren't for every woman, in her opinion they added an "extra element" to an outfit, and she also warned female candidates to avoid wearing too much make-up.

Jabbour said hirers used a person's outfit and general appearance to judge how they would fit in with a workplace's culture.

"Pay attention — don't pull out your old worn business pants and shirt just because you feel comfortable in them, because it can be a sign of laziness, not professionalism," she said.

"Your clothes should be nice, new and clean because employers judge someone based on how they will fit in with the working culture as well as hygiene — that is all part of the interview, and if you look like you're wearing clothes that haven't been washed in a week, that could be a major issue for the team as hygiene is very important, especially in open-plan offices.

"You should have clean and tidy nails with your hair washed and brushed — simple things like that are noticed."