DEALING WITH FIRST IMPRESSION BIAS
Studies have shown a majority of interviewers do not have a scientific way of determining who would do best on a job. Instead, most simply use their own biases to determine whether they think the person is smart and would "fit in" with the rest of the people at the company. Deciding on this basis is really no better than flipping a coin, and it tends to favor people who are good interviewers rather than good employees.
Nevertheless, this is the reality of most interviewing situations you'll run into. As a job seeker, a good way of dealing with this is twofold: presenting yourself well so you can do as well as possible with the interviewer's superficial biases, and at the same time presenting the interviewer with facts and substance that would back up the idea that you could be a good fit for the job -- regardless of whether or not the interviewer asks you to provide that information. The second point does not mean you should be disrespectful with the interviewer; this could cause you to score low marks on their superficial grading scale. Rather, you will often need to take some initiative to steer the conversation in a direction that would give you an opportunity to share facts that would bolster the case to hire you.
CREATING A GOOD FIRST IMPRESSION
There are several things you can do to create a good first impression:
1. Have a good looking, error-free resume. Even before the interviewer meets you in person, they're starting to form a judgement of you based on your resume: its content, writing style, whether there are any spelling or grammar errors, etc.
2. Look nice - wear a neatly-pressed business suit and a classy tie. Make sure your suit and shirt fit properly. The biggest giveaway that you're wearing a cheap suit is if it doesn't fit well. If you can afford it, accessorise your outfit with a nice tie if you're a man, or if you're a woman, a scarf or comparable accessory. You want to give the impression that you're doing well.
3. Control nervousness - it's natural to be nervous on an interview - just about everyone is. But you should take steps so the nervousness isn't apparent. Doing mock interviews with friends or family members is a good way to increase your confidence. The more you're exposed to interviewing, the less nervous you'll be about it.
4. Sharpen your wit - Interviewers often decide how smart someone is based on how witty they are. There is probably no real scientific formula for becoming more witty. However, people who are well-read tend to have quicker wits than those who aren't.
5. Be prepared - if you have researched the company and the industry ahead of time, and you have a good idea of how you can answer most of the standard job interview questions they might ask (such as "Where do you see yourself in 2 years?), you'll be much more confident and your preparedness will show.
HELPING THE INTERVIEWER GET TO KNOW YOUR ABILITIES
Many interviewers will try to classify you based on broad information such as the number of years of experience you have, where you went to college, which industries you worked in, etc. The reality is this information may or may not be a good predictor of whether you can solve their business problems, which is the real reason why they are looking for a new employee.
As a job candidate, it is reasonable for you to want to know why the company is looking to hire someone and what business problems they hope to solve with the hire. The answer to those questions should help you relate to your own work experiences and hopefully give you an opportunity to talk about specific things you have done in the past that have given you expertise in the areas necessary to solve the company's problems. If you offer the interviewer your perspective as someone who has expertise with the specific problems they want to resolve, and strive to provide them with helpful insights that they may not have considered before, you will stand out as a candidate.