Manual focus

Autofocus fails in predictable places: low light, low contrast subjects, anything behind glass or a foreground object, and any shot where the camera guesses wrong about who matters. Manual focus removes the guess. Set the distance once, mark it if you need to, and the shot stays where you put it for the whole take. For a static talking-head setup this is the safer choice, since autofocus hunting mid-sentence ruins an otherwise usable take and you cannot fix it later. Use focus peaking or punch in to magnify before you roll, and check again if you move the chair.