White Balance Preset, if your camera has it, is perfect for when you have mixed light sources or when absolute color accuracy is a must. Essentially, you’re calibrating your camera’s WB to the exact lighting. Although it’s used mostly for indoor shots with mixed light, some people use it for all their shots.
You’ll need to use some sort of calibration target to get accurate, consistent results. Either solid white or 18 percent gray works perfectly. Place the target in front of your subject, fill the frame with it and use your camera’s measuring function to set the WB. You’ll need to review your manual (you CAN put your hands on it, yes?) for the exact steps to use with your camera’s WB preset function.

There are a number of devices made just for this purpose. Some of them are:

WhiBal cards – available in various sizes, from pocket size on up.
Lastolite EZBalance – standard 18 percent gray, popout reflector style.
Photovision Targets – new style with white, black and gray sections. Makes post processing color correcting easy.
ExpoDisc – a device that fits on the front of your lens. Used by many professional photographers.

Use whatever method you feel comfortable with. Again, remember to recheck the WB if your lighting changes. And set it back to your normal setting afterwards.