Practice for the real thing.
This is discussed in a great level of detail, beginning with the philosophy of camera placement:
"There are two approaches to camera placement when you are filming interviews, each reflecting a quite different philosophy of the interviewers function." Rabiger goes on to explain his belief that an 'off-axis' interview proves to be redundant unless the interviewer has a significant contribution, adding also that it is his personal belief that this is often the result of an interviewer who wishes to appear within the film.
After reading this, and having difficulty relating to Rabiger's justifications, I decided to reseach from another source regarding the off-axis interview. I recalled some of my early research on Cinematography from the Focal Press Publication Cinematography: Theory and Practice, where the author argued that within films, it is a golden rule for the subject not to look at the Camera: it was referred to as 'breaking the third wall'. The traditional off-axis approach is to be my preference: if doing so, it is fundamental that I alternate the direction the interviewees will be facing.
An accessible explanation of the off-axis approach can be found here.