-Few polygons as possible.
-Use N-side rather than circles for your sweep nurbs and watch the type of spline interpolation you have.
-several objects under a single hyper nurbs is better then each under their own.
– Omni lights with shadows are slower to render than spot lights with shadows.
-Area shadows may look nice but are very render intensive.
-Reflection, fresnel, refractive and transparent textures add to the render time.
-Bake ambient occlusion
-use traditional lighting over global illumination.
-Displacement in a texture can be very slow to render.
This list can go forever the best is to optimize everything a little bit but you will have to sacrifice quality for speed eventually.
/randy