Okay, let's be frank about this - if you look and act the part then you stand a high chance of beating the competition. Dressing for success is critical to making the right impression. Turning up to an interview with an obvious hair disorder that's quite possibly been created by placing your fingers in a plug socket, or wearing shoes that look like you've just walked to the interview from 100km away will all cause concerns.
The first person who needs to be open to change is you. If you've had the same wardrobe for the last five years or you think your "Christmas piano tie" will win you some well-earned points - you'll need to seek help. No matter how high you regard your fashion sense, it will reap dividends if you gain advice.
Don't always rely on your partner or friends, they will often be biased;and may not want to hurt your feelings. Ask people you trust who will give you frank advice, no matter what they feel. Perhaps ask someone who knows about business fashion such as a respected clothing retail shop. Yes, they'll try to sell you everything but if you leave your wallet behind, you'll get some wonderful free ideas. Shop around for the best suggestions and then work out some budgeted ideas.
Just because you are going for a job as a construction manager, doesn't mean you can turn up to the interview in your overalls and a hard hat. Nor should you think its fine to dress like Australia's next top model for a front desk reception role. You'll be surprised just how many job seekers presume it's okay to go casual or just get it completely wrong for the role.