I think when you make a 3D-render you have to  think more like a painter than a fotographer. The great painters of the past like Rembrand and Da Vinci didn't had any foto-references. They made their paintings by observing the reality, the light, the colors, the composition, the posture and anatomy of their models and put that on their canvas, trying to make a painting that reflected reality.

Trying to make a 3D-render that looks like a foto is imitating something that isn't always reality (or beautiful). Compare your everyday vacation pictures with foto's of some famous fotographers and you know what I mean. Above that many professional fotographers retouched their pictures, and today with photoshop it's more rule than exception, just ask any Playboy-fotographer. (Speaking about what's real and what's fake!)

Some years ago a CG-artist made a render that looked like a crappy foto of his girlsfriend, he had to show his wireframes to prove he wasn't cheating, although everything was wrong on that picture: the lighting, the pose, the scene. It were just the details that made it look real: an old calendar on the wall, cloths on the floor and all kind of littering we see in everyday life and we won't see on professional foto's for advertisements and magazines. It are those kinds of things that cheats the eye and makes our mind believe it's reality. Perception of real life is more than a realistic skintone, which is just one aspect of what makes a good render.

best regards,

Bopper.

-How can you improve things when you don't make mistakes?