Some of the 'bumpiness' will go away with time and practice as you learn to be consistent with the pen pressure as you sketch (I didn't fiddle with anything on my pen settings: it's all default). Another piece of advice I can give, is to do only short, quick strokes, especially when roughing out your drawing. As you get more practice in, things will get smoother on their own and you can do longer strokes.

However, if you really want nice, clean lines, use the pen tool to trace, then stroke the path. Up to you though, as I personally usually only outline with the pen tool for more inorganic objects.