Always use at least two cameras. Having multiple angles makes the editing much easier. You can easily cut the interview and jump from one camera to another during the transitions. Cutting interview filmed with one camera creates distracting jump cuts. Additionally, having multiple camera angles makes the video more dynamic. Sometimes, I even add a little slider movement to add more dynamic feel to an otherwise static shot.

The sound quality is huge. In my video production I use high end lavalier microphones. The lavalier mic is close to the subject and you get much more voice signal and less environment noise. Truthfully, most viewers watching these types of videos will not be able to tell the difference between a video shot with a $30k camera and something nope shot with a smartphone. However, bed sound is immediately noticeable. Bed sound screams "amateur" video. If you don't have a good lavalier mics you can use a shotgun mic. Ideally, you want to get the microphone as close to the subject as you can. You can mount such microphone on a stand and run the cable to the camera. Mixing of the sound is also crucial. To get that professional sound quality you always want to add a little compression to the sound, so the loud parts are attenuated and quite parts are turned up. I often use a little EQ to remove the low end of the sound spectrum. When mixed with some music, the voice that is compressed and lightly EQ will cut through the mix easier.

Lastly, to make a video interview engaging you need to have something visual to cut to. Often this is called B-roll. B-roll shots are visuals scenes that support the story the subject is telling. However, sometimes I use photographs from the subject and build a collage that visually tells the story. When I do this type of a collage, I actually prefer photos that are not taken professionally, as they better represent the reality of the person being interviewed.