Windows are a great place to take pictures!
A couple of tips:
1. North- or South-facing windows are the best, because the light is indirect and diffused. We don’t have any of those, though — our house faces East-West. So instead, I have to wait for cloudy days, so the sun doesn’t shine in directly.
2. Clean your windows first (oops! LOL).
3. It looks best if your subject is looking into the window at an angle so you can see the catchlights in the eyes.
4. Be careful not to block the light with your camera!
5. This method works great if you want to throw the background into shadow. For example, if you happen to have really dated ivy-covered wallpaper, window shots can be a good way to avoid getting the background in the shot. Ahem.