To begin with, pace a scanned pencil sketch by navigating to File > Place and select the sketch file. Here I have used a 72 dpi greyscale scan.
Use the Pen tool to trace the scan. Use a colour stroked line. It’s easier to see. It is good to close all the paths so that each piece becomes an individual complete shape.
Remove the sketch as you finish the tracing.
Delete the stroke and fill everything with black colour. Select all the shapes and go to object > offset path and set it to 1pt. you will get a copy of the shapes which are 1 pt smaller. Fill the new shapes with white colour.
Using the offset path give more thickness to the lines. Scale the new black shapes to give the bring variation to the weight of the lines. Zoom in to make sure that the pieces are in place.
If all the black and white lines look right start the colouring. Add basic flat colours to the white shapes.
Now, using the Pen tool, start to make the shadow shapes. Close the path to make them complete shapes.
Navigate to Window > Pathfinder to make sure the Pathfinder palette is open. The Pathfinder tools are used to combine or cut up two separate shapes. Here I have used the Intersect Shape Areas.
Duplicate the orange shell shape. Choose the orange shell and double click on the rotate symbol in the tool bar. A dialog box opens. Set the degrees to 0 and click COPY. A copy of the shell will be created at the same spot.
Choose the shadow shape and navigate to Object > Arrange > Send to Back. Now select the orange shell too. Move to the pathfinder palette and click on Intersect and then Expand. Now the two shapes will get intersected thus by creating a new shape. Fill this shape with a dark colour to make it look like a shadow.
Repeat the last step with the yellow body, the eyes and the dropped shadow under the shell.
If necessary add highlights to the image.
Hope this tutorial will encourage you to create more cartoon characters.