Step by step
Open up Adobe Illustrator and import your scanned sketch. Go to File > Place to link your image file. Reduce the opacity slightly, then press CMD+2 to lock the object in place. Grab the Pen tool and begin tracing around the outline of the whole character.
Once the outline is complete, increase the stroke weight to 5pt, and align it to the outside.
Continue working with the Pen tool, this time use a medium stroke at around 3pt to fill in the inner detail lines. These paths can be left open ended. Use the Direct Selection tool to go back and tweak the position of the end points so they flow seamlessly from the existing lines.
When drawing paths with spiky sections of fur, sometimes the spikes will be squared off. To fix this, just grab the Direct Selection tool and make some microscopic tweaks to the points.
Use the inner detail lines to separate the body from the legs and the legs from the feet.
Solid shapes can be used on the feet to give definition to the paws. A black fill will merge seamlessly into the thick black outline.
The next set of detail lines are even thinner, at a 1pt stroke. These lines can be used to fill in the finest details such as the eyebrow outlines.
Now the linework is complete, we can start adding some colour. Start with a complete fill by roughly outlining the character. Keep the pathline within the confines of the thick black outline stroke. Use the shortcut CMD+Shift+[ to send the fill to the bottom of the stack, or set up layers to separate the linework and coloured fills.
When the coloured fill layer is placed underneath the linework, the rough outline is hidden by the black lines. Add extra colour fills to the character where necessary, the eyes in particular will need a white fill.
This would be a good opportunity to bring the eyes to life. Draw a large black oval, then add a couple of specular highlights to each eye.
Add a little depth to the character with some subtle gradients. Trace new shapes over specific areas that require highlighting, then adjust radial gradients to flow from a slightly lighter tone to the solid fill colour.
The imaginary light source for my character is in the top right, so gradient highlights are added to the top and right hand areas of the character head and body.
Next we'll add some shading to the character using the Pen tool to draw black shapes. Roughly trace the outline within the black outline, then smoothly cross the body of the character following the imaginary contour lines. Adjust the Transparency of these shapes to Multiply at 20%.
Continue drawing shadows across the bottom left of the character. Areas that cut across the body can are given some curvy lines to both add visual interest and to subtly represent the layers of fur. Shading over the body is reduced to 10% opacity to avoid being too harsh and contrasting.
Shading is added to the underside of the body, each paw, the lower edge of the tail and below the large flappy ears.
A few extra highlights help add more variation in tone to give more depth and dimension. Flowing shapes are drawn across the character but this time they're filled with white and a transparency of Screen at 5%.
The shapes of the highlights can help define the contours of the body, or can be made to follow the shapes of the black outline.
Shadows were added to the bottom left of the character, so highlights will appear on the top right of each of the character's body parts.
Draw a circle and fill it with a black to white radial gradient. Change the opacity of the white stop to zero so the gradient fades to transparent.
Squash the circle and move it into position as a shadow underneath the character.
