Dressing to get the job
As first impressions go, job interviews are complex and have a lot of different parts that job seekers need to pay attention to: answering questions competently, capturing and maintaining positive attention, having a solid handshake, being witty and personable, ending the interview confidently and exiting gracefully, just to name a few. Each aspect of the interview supports the others, so being amazing in one area can make up for being average in another. This is why dressing appropriately to a job interview is so important.
As a former hiring manager for a call centre I have seen the best and the worst in terms of job interviews. While outfits would never persuade me to hire a candidate, outfits often told me a lot about the candidate's attention to detail and how they approached the job they were being interviewed for, which could be the deciding factor in a hire.
What I, and many other hiring managers, look for is three fold: has the candidate dressed appropriately for the company or position, are they neat and clean, are they wearing clothes that fit and suit them. If the answer is no for any of these questions then what does that, combined with the rest of the interview, saw about the candidate. For example, is he or she overdressed, and is it because they haven't had a lot of experience in job interviews, that's what they are used to and comfortable in, or haven't done much research on our company or the position they're applying to.
To know what to wear I suggest you try to find out the dress code of the company. I would always make a note of a candidate's attention to detail and willingness to make an effort if he or she asked me over the phone what sort of dress code we had and what they should wear. When you actually pick out an outfit, and you should always pick out an outfit in advance so that you're not stressing the morning of and you have time to make sure it fits, a general rule of thumb is to dress a notch above the dress code. If the hiring manager says khakis or nice jeans are fine, make sure to wear dress pants; if it's business casual wear a jacket. And when you are invited to a second interview, show you're serious by dressing a notch above what you wore to the first interview.
Having an impeccable interview outfit that is appropriate to the context of the interview is a great and necessary tool to complement your talents and skills and to landing that perfect job. However, while excelling at one aspect of an interview can support others you struggle with, one part cannot replace another. Dressing to kill may initially impress the interviewer, but if it becomes clear you don't know what you're talking about you won't get the job. Vice versa if you look sloppy and completely unconcerned with how you appear to others. You shouldn't rely on looking good in an interview, but it could mean the difference in convincing the hiring manager of your intent and interest.