Here is a tutorial on how to improve the realism of metals (and other similar materials). Compare the left and right images. Which looks more real? The right you probably say and would be right. The way light reflects off the surface is more correct. This tutorial explains how to achieve this.
This is a tutorial dealing with altering the diffuse and ambient amount channels to control the apparent curvature of a surface in conjunction with reflectivity.
This is a tutorial that discusses how to achieve GI (global illumination) caustics from an HDRI image when rendering with raydiosity. It also discusses how to tune the raydiosity cache system to get nice caustics.
This is a tutorial designed to show how to model, UV unwrap and texture a simple paper bag type of object. It is modeled in Strata3D 6.1, then UV mapped in Wings3D.
This video explains what the specular parameter is in the materials dialog. This will help you to understand how to use it, along with the Smoothness parameter which influences it.
Here are two videos which show how to control the lighting in a scene by adjusting several material channels. The diffuse and ambient amount channels govern how much light is absorbed or reflected back to the viewer. These videos show how to use them.