Tonal Drawings - Light Source and depth

We have been working at getting our shading correct so our objects look realistic and occupy space - adding depth. 

TONE: 
The point is, you need to make sure you are creating a depth of tone (black where it needs to be, white paper where it needs to be).

Things you can practice are:
1) creating a gradient on paper with your pencil.
2. Pick your light source and make sure you are consistent to where your shadows and highlights would be. 
3. Shade from dark to light - avoid adding an outline to your image as this will flatten it. 
4. Implied lines are a wonderful thing - once you get to your lightest part just let the eye do the rest of the work.