To save time only render a preview in smaller output size 640 X 480. When making previews you can also use "render cropped region". Only use shadows, in final render. Use ray-traced reflections and refractions, when it is needed, namely in scenes with water, marble, glass and mirrors. Shadow mapping display more soft edges and require less rendering time. Ray-traced shadows have more accurate and hard edges. The ray-traced shadows also transmit color from transparent and translucent objects. However this shadow setting require more rendering time. Use only 1 or 2 lights in a scene. The excepting is indoor interior, where is many lamps and spotlights. Only use sunlight in a outdoor scene. If using sunlight, then adjust light intensity, time and date depending on the atmosphere you want to set. Use the necessary time to adjust falloff angle in cone of spotlight, light intensity and the angle from light source to target. Some scenery require that you combine point light with spotlight.
Read also web page about Rendering and Visualization in AutoCAD 2007
Type OPTIONS enter, click on System, then click on Performance Settings. Click on the small "check box" Adaptive degradation, so that it's ON. Next "check" all items below. In the dialog box "Adaptive Degradation and Performance Tuning" click Manual Tune. Next "check" to enable hardware acceleration and reset to recommended values, continue clicking OK, until you have exited all dialog boxes.
Benefits of using 3D Solids
There are certain benefits when you use 3D solids. From 3D solids you can read mass, volume, centroid, moments of inertia, products of inertia with the MASSPROP command. This information is not possible to get with a box build with surfaces. The exception here are regions. From these you can read area, centroid, moments of inertia and product of inertia. And it's easy to edit a solid with grips. Moreover, you can easily create holes, fillets and chamfers on a 3D solid. Additionally, you can use boolean operations on solids, like intersect, subtract and union. My advice: Always use 3D solids or regions, when it's possible in AutoCAD. In architectural design, use region for the floor. Because it's easier to get the area with the Massprop command.