What is the best approach to sculpting with reference images

I was thinking that the best way to sculpt a head was on top of the reference image but, I seen a video where that was done (https://www.youtube.com/watch?v=IaWxBvlLyr4) and the end product looked nothing like who was portrayed in the reference photo so; I am asking what steps do I need to take make a more accurate rendition.

Nobody answered but today, after the Blender revolution (2.8), it would be very useful to get a good answer!