Window Light
One of the best sources of light for in-home photography comes from windows. Windows that face east and west receive wonderful light during the morning and evening respectively. The quality of window light ranges from soft and ethereal to directional and harsh. To tame harsh window light, drape a translucent cloth or sheet over the curtain rod and let it hang down in front of the window (or tape it directly to the window). Use another sheet or large white piece of paper (tape several together if necessary to get the right size) to bounce light back onto the subject. Play with different reflectors, including aluminum foil and mirrors, to see what effects they have on the subject. Window light makes for the most versatile indoor light source.
Existing Light
Standing lamps, overhead hanging lamps and even ceiling lamps have possible applications as indoor light sources. Remove the lampshade and use the bare bulb to add more light to a room. If the indoor light overpowers the outdoor light, remember to adjust the camera's white balance for indoor lighting (unless the camera does it automatically). Buy higher-wattage bulbs to place in lamps just for photographic use. Architectural photographers occasionally use high-wattage light bulbs to balance indoor light with outdoor light. Also, try changing the color of the bulbs to create a different mood in the room. Blue bulbs create a cooling effect while red bulbs make things look warmer.
Flashlights
Use a flashlight as a direct light source on small objects or to light a particular part of a room. Shine a flashlight through a white cloth or sheet several feet from the subject to create a soft indirect light source. When taking an indoor portrait, have someone point the flashlight from above and behind the subject to create a "rim" light on the subject's hair and shoulders. This technique separates the subject's tones and form from the background. Create a ghoulish portrait light by having the subject hold the flashlight under his chin, pointing the light toward his face. This creates dark shadows on the face reminiscent of classic horror movies.