The Retina II viewfinder does not have projected framelines, so the actual framing of the picture you take is a bit imprecise. To get a feeling, place your camera on a tripod, look through the viewfinder, and move your eye. You will notice that the "framed" part of the scene changes. In my experience, if you move your eye close enough to the v/f that the round lens lets you see 100% of the (blurred) rectangular frame, and you keep your eye centered (do not try to "peek into corners") the framing is pretty accurate. The good news is that a portrait (what I understand you want to do) does not depend critically on framing (versus, e.g.: architecture, abstract graphics).

1. move your camera slightly up and to the left after you have framed your picture.
Comment on quoted advice. Don't try to actually shift the position of your camera; rather, make a mental note of where on the subject you want the center of your picture, and tilt-aim "slightly up and to the left", as reckoned on the subject.
Shifting the camera is in principle preferable and provides a complete correction of parallax, but requires a mechanical device that moves the camera in a strictly parallel fashion. I have such a device called Paramender for my Mamiya two lens reflex. Needless to say, that is not for candid shots!

Another piece of advice: make a test film, taking notes about the extent of the framing for each shot. Then compare with what was recorded on film. From my experience, it's not that bad.