Some of the specifics I'll touch on are:
Max Quadtree Depth
Raytrace Maximum Depth
Raytrace Attenuation
The first two topics are simple adjustments that don't significantly impact the look of your scene, but Raytrace Attenuation not only affects performance, but also has some adjustments that can enhance the the look of your scene.Raytrace Maximum Depth
Raytrace Attenuation