Great drawing! I think the line quality in this example is quite good, as it has a nice looseness and taper to it already. If you would prefer it less thick, I would suggest starting out your drawing very lightly, and only adding the dark outline for it once you are already certain of the lines you want to put down. Also, continuing practice of Warmups to Improve Line Quality before you draw, especially the Light, Medium, Dark Lines exercise can be a great tool to keep improving and gaining confidence in this area. Hope this helps!