Although there are many ways to adjust for white balance, one of the absolute best ways that I have found is to use a Digital Calibration Target available from Photovision.
They come with a DVD that will explain White Balance much better than any camera manual explains it. And they plain out and out work.
They also help you to get perfect exposures every time, even if you think you are getting perfect exposures, you may not always be. These devices help you to make a Histogram that will tell you if you are getting a perfect exposure. Photovision is an outfit that is geared towards portrait photographers, but their Digital Calibration Targets work for any kind of photography and they are relatively cheap at under $100. With that you get a target and the DVD which is well worth it.