How to render in AutoCad ?
I'm not quite sure about AutoCAD 2012 but it will be quite similar to 2011.
Open your part in AutoCAD.
Choose line tool.
Make a line below your part.
Change the UCS so the line can be extruded in horizontal plane.
Under surfaces tab choose extrude and extrude it making the floor. Adjust it using Move gizmo.
Now go to render tab. We have to adjust some of the setting before rendering. First of all full shadows.
Now turn on the Sun for realistic shadows. Under material texture turn material texture on.
Adjust the time of the Sun.
Open material browser from render tab and apply floor tile material to the surface.
Apply plastic material to the body or whatever.
Adjust the model.
Now click on the arrow below the render button. Choose the setting of the rendering and then click render button.
The render window will open up and the rendering will start.
Here is my final result. Looks Good!