if you are shooting RAW, the white balance setting is basically irrelevant.
if you are making JPEGs, then you have several options:
- auto white balance all the time (the camera does a good, but not great job with indoor / extreme / mixed lighting situations)
- pick the WB preset that best matches the situation (e.g. tungsten, fluorescent, etc). may do better then AWB, but still doesn't handle odd / extreme lighting situations properly.
- if you will be in a consistent situation for a while or if the shot must be as good as possible, bring your grey card or a sheet of white paper to use to calibrate the Custom WB setting for that situation.
the method you choose will be determined by how much set-up time you have before you shoot and how critical the WB in that shot is to you.