Taking on the same style as the interviewer doesn't work.
Since interviewing is a staged contrived event and since the initial opinion of you is going to be established in the first 15 or 20 seconds of the interview, it is important for you to realize that you should not necessarily take on the demeanor of the person you were interviewing with. In the initial parts of the interview you must come across as energetic, assertive, and confident. So, no matter how laid back and relaxed a hiring authority might seem, you have to be energetic and enthusiastic in the initial part of the interview.
I can't tell you how many candidates over the years have performed poorly in an initial interview, and I've had my client, the hiring authority, say something like, "Well, Tony, the lady just didn't show any energy or enthusiasm. She was just way too laid back." And when I ended up checking with the candidate, she would say something like, "Tony, that was the most laid-back, low-keyed, unimpressive, slow-moving person that I ever interviewed with. So, I simply mirrored and matched his personality. I can't believe that he said I was laid back with no energy. I took on the same personality that he communicated."
The initial moments of the interview have to be performed on your part, with energy, aggressiveness, and confidence. Even if you think that you were being much more aggressive and assertive than the person doing the interviewing, you have to be this way. The interviewing authority is comparing you with the dozens of others that she might be interviewing. You have to set the tone of energy and confidence.
Sometimes taking on the style of the interviewer does work.
As mentioned above, since interviewing is staged, you want be the first one to be aggressive and get the attention of the hiring authority. A forceful, enthusiastic presentation of yourself does that initially. However, after you have the interviewing authority's attention and rapport, you may begin to establish deeper rapport by taking on the style of the interviewing authority. The purpose of building that kind of rapport is to "lead" the interviewing authority into being more "like" you.
So, after you have gotten the interviewing authority's attention and interest, you may build rapport by "mirroring" his or her style. So, if she leaned back in her chair and crossed her arms, you do the same. If he talks in low tones, you would do the same. However, you would only do this long enough to build rapport. Once you have built that rapport, you can "lead" the hiring authority to take on your style. The ultimate compliment of building rapport is that a person mirrors your style.
Telling stories bypasses conscious resistance to hearing the point that is being made. Stories are powerful. They remove people from their personal prejudice and get them to mentally and emotionally focus on what you are saying.
Have stories about yourself. They need to be relevant and specific to issues about your being a good employee. Keep them short and relative to the topic.
The ideal use of a story is to answer a question, then add a little story. For instance, you are asked, "How do we know you are a good worker?" Answer, "I have worked hard all my life. While in college, I held three jobs. I was a resident assistant in the dorm, I sold life insurance, and delivered pizza on the weekends. All this while maintaining a 3.2 grade point average."
There will be resistance to and fear of you as a candidate. When you tell stories in the interviewing process to support your features, advantages, and benefits, you remove the natural fear to hiring you. For example, Jesus Christ, and every great teacher, led people to believe by telling stories and parables. Don't go overboard here, but three or four stories that prove you are a good employee, that bolster what you're saying in the interview, will always set you apart from your competition. Remember: Stories sell!