The Rule of Thirds, is one of the absolute basics in filming and cinematography. It is based on the so-called "golden ratio" and states that a picture has a particular aesthetic effect if its main motif is placed on one third of it, viewed both horizontally and vertically.
If you are filming a person, you should make sure that your model is vertically divided into three in the picture. The eyes should usually be on the upper horizontal line. If you now make sure that the interviewee is looking into the picture, i.e. the long side of the picture is in front of their face and the short side is behind their head, then you get the professional picture look that you see in films or documentaries knows. You've now placed the person in your picture using the Rule of Thirds!