Two step by step walkthrough examples of how I cel shaded items. The art is a little dated, but the method I use is still similar and this should still be helpful regardless. 
The important thing is to keep in mind light source and to have it be consistent throughout the item, it's varying forms, etc.
View attachment 133
View full guide
The important thing is to keep in mind light source and to have it be consistent throughout the item, it's varying forms, etc.
View attachment 133
View full guide