One way of viewing negative spaces are to place objects inside a rectangle drawn on a piece of paper then draw the shapes around the objects.
Another method is to cut apart a magazine photograph or photocopy a drawing by a master artist. Reassemble the negative space pieces on a sheet of black paper to observe the outline of the original object.
To help you view and draw negative spaces, you will need a viewfinder. Take a piece of cardboard and cut out a rectangle in the center in the same proportions as the paper. The rectangles should be about 1" x 1.25".
Hold the viewfinder in front of your scene (for example, a chair), preferably with one part of the main object in the scene touching the edge of the viewfinder. Now direct your gaze at one of the negative spaces rounding the object and observe the shapes. Make a drawing of the negative spaces.