I found the process for making these designs very satisfying. 

I start with a line-sketch but quickly move onto finding a 2-value representation, finding the simplest differences in material that make the character read. 

Then I shade the character with a clipping-mask layer set to Multiply. Since this blending mode proportionately darkens layers below, it sections the design into 4 distinct values. With the background they add to a total of 5 distinct values.