Ok, my thoughts.
THE RESUME
I think the process of the job interview begins with the resume. Unfortunately I don't have experience in being able to pick the resumes, but what my sense has always been is that you want a resume to stand out. Many jobs will make you fill out their resume template and I understand why in technical fields that may be beneficial, but I don't like that.
The resume can tell you a lot about the person. My resume for example includes a headshot of myself and is colorful with borders and fancy headings and lots of other bells and whistles. It has given me a huge advantage over other candidates- I am almost always told by the person interviewing me how it stood out and impressed them. Many people put 'references available upon request' but I always give my references along with letters of recommendations and other backup documents. It may seem like overkill, but my feeling is, I am trying to show who I am, which is a very detail oriented thorough person, and I am trying to find a place to work I want an employer who is going to be looking for ME, not somebody I'm masquerading as.
THE INTERVIEW PANEL
The structure of your interview panel is just as important as the interview itself. I find that it's good to have more than one person present in the interview, even if it is intimidating. Some companies do rounds of interviews with a candidate and this might work for more professional roles where they want to eliminate and only give the 'best' candidates to interview with higher ups.
But I have found this format works, where you have at least one person who is 'at the same level' as the candidate if they will be working on a team, then you have the team lead or whoever they will directly report to, and then the head of the department and in my job specifically, the boss of my boss is also present. So that's usually 4 to 1 but it does work out.
INTERVIEW QUESTIONS
I always keep a list of interview questions, as both the interviewer and interviewee. As the interviewee I tend to go overkill with questions, I make sure I have a ton so that when they ask if I have any questions it becomes like an interrogation to the people interviewing me. I am not sure if this is just my funny bone at play or what but it is actually effective. Many seemed stunned by the technique but in my experience the reaction overall is positive and the person feels I am prepared. I have not seen others utilize this technique to the degree I do, so I don't know how I would react if I saw it.
The quality of questions should be about if both of us are good fits for each other.
Depends on the role but as interviewer I am trying to find out:
Is this person going to stay with the company? (Our roles strive for retention)
Can this person grow in the company?
Does this person fit the culture of the team that we have cultivated?
Will this person be happy in this role?
I will ask a series of silly questions at the end of an interview to display our company culture and try to gauge for if they fit it or not. This also tends to give people a feel-good ending for the interview and a positive impression of our company which spreads, even if they do not get the role in question.
As the person being interviewed:
Are the people interviewing me being authentic or presenting a false ideal of themselves and the position?
What is the company culture like?
What is the turnover rate?
What are the benefits?
How do the current employees feel about the position?
What are the most challenging aspects and are these acceptable to me?
Do I get along with the people that work there in general, especially the superiors?
Is this a place where I can grow, does it give me what I need to be content?
As others have mentioned I find a conversation style interview to be the most effective. You want it to feel organic. Yes, I come prepared with questions but it is never the question you ask that is helpful- it is the follow up questions. Listening carefully to the responses and knowing which rabbit holes to pursue is extremely fruitful. If you can make jokes and get people to relax and share your own experiences and give the impression that you're just a person like them, you can sometimes get the advantage of them letting their guard down.
This is incredibly important on both sides. You do not want stiff professionalism unless that is how it is going to be at the job day after day. You want to get to know this person because if you end up working together for 20 years you're going to want them to be a pleasant person that works well within your company. Nerves and fronts will prevent you from accurately seeing who this person is and often hiring the wrong person.
Ending with when you will contact them about the position and giving a concrete date or timeframe is important. If I am interviewed and don't get this, I ask.
POST-INTERVIEW
Meeting with those present in the interview to discuss pro's and cons of each candidate. If it's just you, taking aside time to do this in a concentrated manner where you are not distracted.
As the person who is interviewed you can send a thank you card for having been interviewed. It is old fashioned and doesn't mean you'll get the job, but again: makes you stand out. Secondly, if they never gave you a time they would get back to you or it comes and passes, CALL them. Harass them. My experience with this has always been positive because it shows initiative. There is no harm in wanting to know if you got the job or not so you know whether to move on.
I might have more thoughts later, but so far, this has been my experiences. I really like interviewing people. I was surprised by that.