When doing an interview there are a few things you need to do every time.
Fill the frame
When doing an interview you need to choose good composition and background carefully. Pay attention to everything inside the frame.
Get tight on the person you are interviewing.
Kill the Noise
Once you have put the microphone in place and have your headphones on you will be able to hear all the ambient sounds. This is where everyone is quite for a moment while you just listen.
Lets say you hear the ceiling fan or the air conditioner running. I would turn these off for the interview.
If you cannot turn off something like a water fall or water fountain, then move to a quite location.
Steady the Camera
Use a tripod or put the camera on a table. Just keep your primary camera for the interview still. If you have a second camera to use then you can maybe do something like putting that camera on a slider or fluid head that will let you move the camera during the interview.
I believe you always need one camera that is locked and on a tripod for the interview.
Light the Subject
My suggestion is to find a great place with light so you don’t have to use lights. I find the open shade on the side of a building works as well as porches as you see in these two photos of interviews we were doing in Togo, West Africa.
Audio is King
There are times for different microphones just as there are times for different lenses. You need to know the difference between a lapel, on camera & shotgun microphone.
Sharpness is Queen
Sharp focus is critical. I advise against shooting ƒ/1.4 for video unless this is your second camera perspective. Have a depth-of-field that is forgiving if the person moves during the interview.
Use manual focus and not Auto-Focus.
Lock Down the lens
Don’t zoom in and out on your primary camera. You can do some of this with a second camera, but be sure at least one camera is locked down and you have a solid framed shot that is in focus and has enough depth-of-field that the person can move a little and still be in focus.