Negative space is most simply defined as "the space around the subject of an image."
I love using negative space in my photos to draw the viewer to what I'm trying to show.
The easiest way to express this is placing a person off to one side of the photo as opposed to centered in the middle. It a traditional portrait? Nope. But does stepping outside of that "traditional" composition make it a bad photograph? I don't believe so!
So go out with your camera this week and try NOT to fill the frame!