I can give you one main point. Lights.
I find it's the lights which will make or break the image, especially if you're after realism.
I no longer render in Poser 7 so there will be better qualified people than me on this. However, I would try using any HDRI or IBL sets you can.
Shaders are important also, the mega bagginsbill should be able to help you on this one.
Pose & expression. If the pose is realistic & the character has a proper expression & not staring blankly into space, this should be a good start.