The default lights have one advantage: They provide a nice, even lighting when posing and settig up the scene...

When it's render time, delete them and set up something else. I have a few "start sets" I have created for different purposes, I load them as a starting point and adjust them for the specific scene. They usually consist of a few white spotlights arranged in a photo studio fashion. From there, I can add any additional spotlights I need for the scene and get a good result.

There are a few tutorials around that deals with lighting set-up, you should be able to find something in the "Poser back room" here by clicking on the Poser Forum banner above. Arranging a simple light set by yourself isn't that tricky once you get a feel for how the Poser lights behave. It takes a little time experimenting, but it's worth the effort!