What is photorealism? Probably the simplest answer would be: "seeing the world as a photographer". So you better become one. There is no better way to achieve photorealism in your renders than trying to be a good photographer first and 3d artist second. This is the way I traveled and I would like to share with you some of my observations. And in case you are thinking about shortcuts...there are no shortcuts, unfortunately. But the long way ahead is very enjoyable!
I worked for many years as a fashion photographer, both with digital and analog cameras, on location and in the studio. I think the best way to teach yourself about proper lighting setups is to log hundreds of hours shooting subjects in the studio, where you are in control and the light is your servant and not the other way around. I will try to point you to the best resources to teach yourself about light and if the time permits discuss common 3d lighting pitfalls that photographers notice immediately that are not so obvious for other people.