Just put your DSLR into live view mode and move through the various WB settings. You can use the usual suspects, like Cloudy, Tungsten, Florissant, but it's really helpful when you start to tweak the Kelvin settings to get exactly what you need. When you get what you want, switch off live view and you're good to go
White balance is very important, especially if you're shooting in jpeg. But it tends to be a bit of guess work and you're never sure of exactly how it's going to look. Well guess what...you can see it in the screen on the back of your camera.