...is to take some test shots indoors with flash at different white balance settings. Start with the flash setting, and vary it +/-3. See which of these you like best, or some other setting. Once you know which setting to use, you can just dial it in for reproducible results every time.
BTW for outdoors, I prefer SHADE+3, unless shooting garden shots, where the cooler CLOUDY-2 gives a little extra boost to greens. CLOUDY-3 is similar in color temperature to SHADE+3, but some of the colors are very saturated compared to the shade setting. It's all personal preference, however. Choose what you like. One of the best parts of digital is you get to choose this setting.