It’s all about Using windows and doorways
When i walk into a groom or Bride's house i take a moment to scout the environment for natural light sources. Windows are a great natural light source. Sometimes it floods the room softly bouncing off the floor and the walls.
Placement of the groom or bride is crucial. 2-3 feet from the window, also experiment with the angle. Often rotating the subject slightly can have a drastic effect in the final shot. I also like to carry a small reflector in my kit to fill in some darker areas if needed.
It's a good idea when shooting with natural light to close all lights in the room. Competing light sources can drastically alter the white balance and colors of your image.
I goes without saying that when shooting with natural light indoors to use a daylight white balance. Therefore stay away from Automatic White balance.
The best results i ever got while shooting a wedding is when i take the time to look for natural light sources. At first it could be frustrating but after some practice you will be able to easily spot the best possible location very quickly. I know that i have personally improved my wedding photos over the years of practice.