Here is a list of factors that increase render speed (make it go slower).
The complexity of the light increases computations and thus render time. Using these economically can help increase render speed. Multiple lights. Each light increases render time almost exponentially.
Number of present geometry and textures occupying RAM and processor speed--The more you have of these, the less RAM and processor power is available for the render engine.
more textures--The file tdlmake has to process each texture in preparation for the render in DAZ Studio. This is the 'Optimizing Image' phase.
Shadows and shadow maps
Complex light effects, like soft shadows, ambient occlusion, reflections, transparencies (or less than 100% opacity).
plugins that affect surface values, like pwSurfaces which significantly adds to render time.
If you are using a plugin for skin or surfaces that increases render time, you may want to consider using Pendragon's Shaders. These are in fact free and can be found in the DAZ Studio forum on our website. These scripts offer a lot of improvement for little expense in added render time.
You can also improve hardware that supports rendering. Add a faster processor or increase RAM (up to 3 GBs). In Studio, you can also use your video card for rendering (OPENGL). This requires a high end video card or a dual card (or even dual SLI cards) to maximize this type of render.
DAZ Studio makes use of dual processor systems. Carrara will make use of dual and quad processor systems. Carrara Pro supports network rendering.