This may seem a bit negative, but as I hiring manager I found the expectations of the candidate usually pretty unrealistic. From experience, the hiring manager has lots of day job obligations and hiring is generally a side show in that circus. I am not saying hiring isn't important. It's actually extremely important, but most managers aren't very good at it and, because it happens sporadically, they don't get a lot of practice.
Resumes are generally not very helpful and consequently most hiring managers don't delve into them in advance. They tended to be conversation makers, 'I see you worked at X' or 'You went to college Y' 'Tell me about that'. I got a lot of resumes which were from people with NO QUALIFICATIONS & EXPERIENCE in the posted position. People would just shotgun out their resumes and see what stuck so that didn't do a lot to build confidence in the value of resumes.
Likewise, the job description provided by the company usually doesn't really do a good or even adequate job of explaining the role and its real responsibilities. That's unfortunate, but creating a meaningful job description (which often isn't the task of the hiring manager) is just as hard as creating a meaningful resume and therefore, it doesn't happen that often.
Skills and technical experience and qualifications are important but the hiring manager is also just as worried about fit. Can you integrate with the other employees on the team, with the other teams his team supports. In my world we support sales people, so I wanted to determine whether the candidate would be able to work with sales, keep their hours, respond quickly to their demands and generally impress them with their credentials. Not all roles are that political but I would say determining how well the candidate will fit in to the company is always important and not often seen that way by the candidate.
I always tried to convey a picture of "a day int he life" of the role for which I was hiring. As a candidate, you should try and get as clear a picture of what that day will be like and whether that is REALLY how you want to spend your time. For example, application programming is hot these days and, at times, I wish my programming skills were better. However, programmers spend the day inside tethered to a computer for hours. In reality I like to get out and meet people. So as much as I romanticize that job, I probably wouldn't be that happy doing it full time. You need to ask yourself, am I going to be happy doing this job day in and day out. That's hard to know as a candidate, but asking the hiring manager and the technical interviewers how they spend their day, what they like and don't like about the job will help you paint a more realistic picture of the role.
Dress appropriately for the interview. Interviews are a bit like a first date and managers expect your attire is going to be 'the best he or she can expect' from the candidate. If that is substandard on the first date, there is reason for concern about the future.
All hiring managers have a problem they are hoping you can solve, There is a gap that needs to be filled and they are actually hoping you can fill it. Generally, if there is an open position they are filling in and shouldering some of that workload themselves. Ask the hiring manager what his or her problem is. 'Who would I work with supporting what external accounts or internal teams?' 'What's the perfect candidate look like?' Think creatively about your qualifications and your ability to step into that role and take that burden off the hiring manager. Your ability to convince them that you can fill their gap is fundamental to getting hired.
Finally, take a look at the book Designing Your Life by Burnett and Evans. There is a chapter on job hunting (7: How not to get a job) and they argue against resumes and the formal hiring process. Their approach makes a lot of sense so I recommend reading that chapter - the whole book is terrific.