Rough Shapes

I started by making the basic shapes using references from Pinterest to for the poses.

 

Sketch

Then I drew details of the expressions keeping it rough and loose.

It was towards he end that I noticed the faces where not symmetrical, the last two where drawn with more care. The others lean slight to the left, which is noticable when I flip the image.

 

Refined Sketch

Next I added more of the facial features as well as the light direction.

 

Line Art

The line art is very loose, knowing I can correct anything with the shading. However not taking the time to make sure the lines where good made the final results suffer.

 

Shading

I used simple cell shading, followed by hatching finishing off by filling the areas where the hatching built up.

 

When I finished the sadness sketch, that I began to push the amount of fill. Because the surprise face was push wide I kept it light, however I think it would have been better to continue to push the cell shading.