Remember that the first shape you draw will be the foundation of your drawing, because you will use that first shape to compare proportions of other shapes. When depicting the initial shape carefully compare the shape's hight to width. Proportions of the initial shape need to be resolved before proceeding to drawing other shapes. At the beginning stages of your drawing you should always compare shapes that are directly beside each other, so that you are building your drawing around and out from that first initial shape. If you are not sure about your initial shape consult instructor. (see example of Negative Space Drawing in video posted on blog below this blog posting)
As in drawings from previous classes once the initial shape is established continue by describing the basic shapes of the entire subject matter (still life). At times you will have to adjust shapes by moving or modifying shapes. Do not get caught up in little details of shapes but instead think about the subtleties of the basic shapes in terms of proportions and in terms of where shapes line up vertical and horizontal to each other. In the beginning stages of your drawing measure with your drawing/painting tool (and/or by eye) to get aquainted with the basic shapes created in the negative spaces.
Once all of the basic shapes in the later stage of the drawing are tentatively depicted consider: comparing size of shapes to each other, carefully check and re-examine proportions and vertical/horizontal alignment of shapes and clarify the subtleties and details of the shapes.