There is a misconception that it is not possible or very difficult to learn to be a good designer. This is simply not true. Like anything, it takes practice. Understanding design is as much about training your eye as it is about knowing the basic principles.
Interpreting negative space is one of the basic foundational pillars of training the eye.
Negative space, in art, is the space around and between the subject(s) of an image.
One of the reasons we innately appreciate negative space when employed well, is that it evokes a sense of balance, the first principle of art.
These two tumblr collections showcase a wonderful use of negative space: