Lighting for any video recording is crucial to how the visuals are going to end up appearing on the screen. When you have the ability to shoot indoors with no outside light you have a lot of control over the situation and how the light is going to illuminate what you are shooting. Once you step in to a room that has the bright light from the sky creeping in through a window you give up some of that control and have to address it in specific ways.
When you are shooting in a room with a window the first thing you have to do is make sure that the light from the window is the "key" light on the subject. This means that the light needs to be relatively bright and reflecting off the side of the face of your subject. You can still use an artificial key light, like a lamp or a Tota light from a portable light kit, but it needs to be lined up with the window. Never try to move the key light to anywhere but in direct line to where the window is located. You should always try and keep the camera about six feet from the subject you are shooting, and give them as much room between them and the background as physically possible. If there are any distractions on the background they are in front of, make sure that is out of focus unless you specifically want the audience to see it.
Put a backlight, or kicker, several feet behind and to the side of the key light. Angle the kicker light to highlight the back of their head. Place the background like directly behind the backlight, pointed at the background from that angle. You usually do not need a fill light, or white card, when shooting in a room with lots of outside light coming through the windows. The chances are that all this light in the room featuring the windows will make the subjects face a little brighter than usual, so you may need to set the camera's aperture setting down. If you have to lower the aperture setting, you must make sure to bring the background light closer to the background otherwise it will appear as though it is not lit. If there is a distraction or object on the background that you are lighting make sure that the background light is distributing a clean, strait beam of light. If there is any design or text on the background it needs to be equally lit or else it will be awkward and distracting.
So the trick to filming indoors with light coming through a window is to be careful where you set your lighting, be aware of any background distractions, and control the amount of light coming through the lens.