Natural light is my favorite light source. In fact, if someone asked I would say I was a natural light photographer. By the way, it’s taken me a long time to finally call myself a photographer. I digress.
When inside it is best to get your subject by a window if at all possible. Interior lights can wash out your subject and typically never allow for catchlights. When I first started out, I thought that you wanted your subject to face the window head on. What I didn’t know at the time was that when your subject faces the window you can get flat lighting. Basically, this means that while your subject’s face is light up there is no depth or shadow. Their face looks flat.
The trick is to position your subject so they are facing the window at a 45 degree angle. Therefore, you can stand next to the window so the light is coming over your shoulder and your subject is facing you at a 45 degree. This allows for there to be some subtle shadows which adds depth to their face.