You have probably noticed that there are many different types of brushstrokes in digital drawing. You have probably seen lines that start heavy and end thin. These are lines are made by the pressure-sensitivity of a tablet. Acting much like a pen, the stylus of a tablet will register the lines as thicker the harder you press down.
Neat Line Art
By this point, you have noticed that there are people who manage to make their line art look neat and clean every time. This is attainable!
Why make your line art clean?
You might be asking why you should make your line art clean. After all, who cares if your drawing has seven or eight lines creating the hair, rather than just one?
The answer is that many cartoons and drawings styles that use line art look better with clean line art. There are many styles that do not use line art, (or selectively use clean line art, or even stylistically use messy line art) so you should not limit yourself to this, but there are more than just stylistic concerns when you draw using line art.
By teaching yourself how to draw with clean lines, you are building your confidence in your drawing skills. Knowing how to curve you line just right will teach you how to get better shapes and achieve the lines in your drawing that you want, without worrying about erasing the extra parts that come with messy lines.
Draw an entire object using long lines as discussed above. If you need to, use your whole arm instead of just your wrist. DO NOT get discouraged by shaky lines and go back to short strokes. Share any tips you found for making your lines smooth, so that others can learn too.
Future use: apply this technique to your pencil and paper drawings as well to achieve overall improvement in your line art.