1. Turn off the lights!
Most artificial light has color to it that can suck the life out of your photos. For example, the lights in our kitchen have a yellow tint to them and they can make everything look yellow. I really HATE yellow lighting in my photos so I always do my best to eliminate it. When I am shooting inside, I always try to turn off as many lights as possible (during the daytime, obviously :) ) This allows me to use natural light coming through the windows.
Mixed light sources (aka window lights plus your table lamp) can also make your photos look flat and can create unflattering shadows.. especially if the light source is directly above your subject's head.
2. Side light, Silhouette, or Front-Lighting
There are several ways to use window light. My two favorite are using it as side lighting (which I do a LOT) and you can also use it to create a beautiful silhouette image. You can also use front-lighting, however, I love shadows so I rarely use this method (it can be very flat with minimal shadows on your subject).
Below are a few examples of side lighting. When side lighting, your subject is perpendicular to the window.