If you plan accordingly, you can create your background separately, then composite it with your main character and give it a slight blur to suggest depth of focus. You can also add shadows and highlights in places where Poser may have, for whatever reason, chosen not to put any. Only other thing I can think of offhand is you can play with colour, desaturate it a bit: real world colour is never as bright and intense as Poser may make it.

docandraider.com -- the collected cartoons of Doc and Raider