Sometimes you will be able to move the people or things you are filming so that some of the brighter light in the environment you are shooting in is shining directly on them (or is not shining directly on them - depending on the light available to you in the scene). It may be a bit awkward at first, but video can last forever and a moment of tension may quickly be forgotten.
If you can’t move the subject, move the light (for example, reposition a lamp or open [or close] a window shade), if possible, or (if you are unable to move the light or whatever you are shooting) move your camera so that the lens is aimed at the side of your subject that is lit by whatever light is in the environment. This is especially important when most of the light is coming in from the windows. Doing this will allow you to see more detail in the video image and make your footage look much better than most home movies.
One thing to be aware of is that many cameras have some sort of auto-iris adjuster built into them. This feature makes the lens close down and not allow as much light in (when the scene is very bright) and open up to allow more light in (when the scene is darker.) This is great when you are in a hurry and can’t set your iris manually, but it is an obvious sign of less-than-excellent camera operation. This is especially true when the iris adjusts several times during a shot. Remember that the camera is automatically guessing what the best iris opening is and it often guesses wrong.
You can learn to take advantage of an auto iris with some practice (using the above techniques) and then develop the technique of setting the iris manually (if that feature is available on your camera.)