Couple of thoughts:
- My work improved the most when I began to explore underlying structures in illustration. A work may look polished and effortless, but there's a world of messy construction that creates a framework to put the pretty finishes over. Looking at your piece, I'm not seeing any evidence of rough drafting, and that's where you build things from the ground up.
- Pencil is not a "clean" media. That's ink. Trying to make pencil work look "clean" is fighting it. That being said, if you want to use graphite pencil as your finish media, you might consider picking up a colored pencil to create that underlying framework I mentioned before. Red or blue is traditional, and you strip them out digitally in Photoshop (it's an easy trick, a Hue/Saturation shift).
- Back when I was in school, I took a lot of drawing courses that I found frustrating, because I misunderstood the value of what was being showed to me. A lot of classes teach you classical "realism" drawing techniques, and that may not be the sort of drawing you want to do.
The trick is understanding that those lessons are applicable to ALL drawing, not just "realism". Composition, Anatomy and Perspective are valuable knowledge bases for pretty much every type of visual illustration you can imagine. When I buckled down and forced myself to learn more about them, I came to understand that these were not lessons in "how to draw", but rather lessons in "how to solve drawing problems". So if you (like me) found yourself frustrated by teachers who insist on teaching you how to draw a certain way, you may want to take another look at their lessons and then compare what you see there with the works of the artists who exemplify the type of drawing you DO what to explore, and see if you can't find common ground.