In this interactive pdf article Miles Waterhouse when and how to apply reflections to car drawings and offers some tips to make the process easier.

This tutorial shows the progression from a line drawing sketch to a final render, with details and changes made during the digital rendering process.

In this tutorial Giangiacomo Barbero goes through the process of creating a presentation rendering with a painted look and a complete surrounding environment. For this image he used both Photoshop and Painter and achieved a dark and futuristic atmosphere.

This video tutorial shows the perspective and sketching process with Corel Painter. It is divided in four parts and is available in downloadable high quality wmv format.

Mini Walkthrough of a render, 3 step sketch and rendering walkthrough

How to make a digital rendering of a car in Painter, starting from a lineart

The basic steps to create a digital illustration starting from a hand drawn sketch