Know light. Use of natural light indoor

If you are shooting indoor you do not always need  artificial light to expose your pictures: you can do a magnificent job using just available natural light. You just need a room with a window and sun light, of course.  You could use the window as a back (or rim) light to create a silhouette of your subject or you can move around and use it as side light: depending on if you expose for the mid-tones or the brighter side of the subjects, you'll get different results.

A reflector or a white board might be very helpful: it's perfect to bounce and soften the light to create a more delicate mood or to fill up shadows; but be careful with the kind of white you are using! some materials, for its composition or the way they have been washed, produce ultraviolet light, resulting in a blue cast in the image. Depending on where the reflector is positioned it will create a different atmosphere. If it is held in a higher position, imitating the sun,  the look will be very natural, if it is held down bouncing up the light, it will create a more artistic effect.

I prefer using north light when shooting indoor because it's softer and I don't have to deal with heavy deep shadows; however there are situations when direct sunlight is more suitable: when you want to play with high contrast or with shadows of the window drawn on the subject, for example.

As always, the key of photographing indoor with natural light is to stay creative: you have to move around, not only to get the best composition, but to see how the characteristics of light change; you have to play with light and shadow, stay alert and take advantage of opportunities: a single ray of light passing through a window slightly ajar it's enough to shoot a stunning image.