When it comes to interviews, everyone does it differently. However there are a few very simple steps you can take to maximise the engagement with your interviewee.
1) Meet and greet!
If you’re on location, you’re busy, but take time to make time. Popping a camera on someone straight away can be quite difficult for most people to deal with. By having a brief and friendly chat before you get started you put the subject at ease and the answers you get will be 100% better and look a lot more natural.
2) Keep the eyeline!
I’m forever finding myself awkwardly stooped next to the camera! By asking the questions myself and keep my eye line level with the lens it encourages the subject to talk more naturally and in a way that looks pleasing.

This setup shows poor eyeline, facing up and away from the camera. The green line shows where the subject should have been looking.
I’ve seen a lot of otherwise great interviews spoilt by not following this rule. If you’ve gone to the effort of getting the exposure, white balance and framing just right why undo all your good work by having the interviewee virtually talking off camera?
3) Include the question with the answer!
Be prepared to ask this one a lot! Unless you’re dealing with a pro, people tend to jump in with answers straight away. Ask your subject to wait a beat before answering and then include the question in their answer.
What tends to happen:
“What’s your name?”
“John.”
What you need to happen:
“What’s your name?”
“My name is John.”
Don’t be afraid to jump in and make sure you get it right. It’ll save a lot of headaches in the edit.
4) Alternate shots.
A lot of people think this only really applies to the corporate model of interviewing but it can be just as effective in vox pops. Especially in situations where the number of cutaways you have is limited.
Capture a couple of answers in CU and then a couple of more in a mid-shot. As long as there is a big enough difference in the framing, they will cut. If the interview is long, it can also help build the pace of an edit, so get a couple of frame sizes – there really is no reason not to.

Two frame sizes can help build the pace of an edit, and give a 'jump cut' option when shooting vox pops.
5) Mic Placement!
Much more important than it sounds! (Pun intended)
If you are using a boom or a top mic, so be it. But if you’ve decided to rig the interviewee up with a decent wireless or lapel mic, go to the effort of hiding it. It just looks messy and has a very jarring effect on the viewer.

Two examples of mic placement. The right hand frame looks messy and is easily avoided.
Monitoring the audio is a whole subject in itself, but keep the headphones on during the interview and be vigilant for cracks and pops in the audio. If a question needs to be asked again because the subject touched their tie then so be it – audio is a major factor in any production, make it count!