the indirect light filtering in through a window is bright enough that you can take a shot without using flash and it is really lovely and flattering to skin. flash is often quite harsh and flat on the skin, while window light is soft, gives more natural skin tones and creates lovely shadows and higlights. these two shots were taken at the same time of day, and processed the same way. the first one was in a darker area of the house with flash, the other was taken about 2m away from a big window.
the best part of window light is that it gives you the most gorgeous catch-lights in the eyes. catch-lights are those pretty reflections of light on the eye that just make the eyes sparkle. you can see from the examples below that flash does not give a pretty catch-light at all; it gives a little pinprick of light, usually right on the pupil that is not very flattering. in addition, when there is plenty of window light the pupils are smaller and you can see the beautiful eye colour more clearly.
so turn off that flash, hang out by a window, and capture those gorgeous catch-lights =)