Adobe Illustrator CS3 has built in so many tools so that you don’t have to waste time trying to create your own techniques anymore. One of the ones I love is the built in gradients. If you have a vector art image that you pull in to Adobe Illustrator simply click on the image. Go to Window, Swatch libraries, and choose gradients. There are a bunch to choose from so I would start with “Earthtones.”
While the image is highlighted simply click on one of the gradients and viola! You have a great gradient for your image. If you want to change the direction the gradient is moving in, then choose the Gradient tool from the tool bar and drag your mouse from any direction on the image after you have picked a gradient and you’ll be able to have a more precise design.
Also, if you want to change more specifications of the gradient, then go to Window, appearance, and you can change each individual attribute of the gradient.