Let's try to create a nice seal drawing filled with simple shadows and basic colors! To do so, you will need a vector application as well as a pencil and a piece of paper. The cartoon character is quite easy to reproduce as long as you take your time. Let's move on to the first step!
Start by sketching the seal on a piece of paper. Feel free to experiment or even try your own version if you feel comfortable to. Once the character is done, scan the illustration (or take a picture) and open your vector software.
Import the illustration in your application and add a new layer. Draw dark outlines on the layer using simple lines (with pointed ends if possible).
Next, create a new layer behind the one used to form the outlines and draw plain shapes filled with grey colors. The eye can be white while the pupil must be black.
Select the gradient tool and add a second color on shapes created in the previous step. A darker version of the grey used on the plain shapes is perfect.
Using the gradient tool didn't create a very convincing shadow on the seal drawing. So it might be a good idea to manually create new shapes that will be used to enhance the depth of the cartoon character. Add a new layer between the one used for the outlines and the other one used for the plain shapes and draw darker shapes as shown above.
Use transparency to partially hide the shapes created previously. These stronger shadows are nice, but there is one last thing that we can do to give more volume to the character.
We can add reflection. Indeed, light is usually creating lighter areas on the body of the seal and we will duplicate this effect by drawing large white shapes. Pink areas must be white too. I used the pink color to make sure that you could read these shapes easily.
Of course, you also need to use transparency to partially hide these new elements. It's important to keep the top of each shape white and light.
One last thing we can do to improve the illustration is modify the color of all outlines. I have picked a dark grey color for all outlines except the eye and the pupil.
Good job! Your seal drawing is now finished and you can proceed to another character if you like to! :)