First thing's first: excellent work! Most artist's don't make it this far with their work and it's always nice to see another newcomer putting their ideas into the world. In addition, you have an excellent sense of motion in your art and I definitely appreciate that. It's a quality I wish I had a better grasp on,
That said, there is definitely room for improvement. There's a lot of white space on your pages. They feel more like preliminary sketches. With pencil or charcoal or chalk, it's important to remember that you've got an entire spectrum of grays to work with, not just the gray produced with your natural pressure. I'd recommend practicing a style called "chiaroscuro," which is all about over-emphasizing shading, and then tone it down a bit from there in order to find the style that fits yours best. Also, some of your proportions seem a bit... off. I know many artists, myself included, have struggled with this issue many times in the past, so I'd recommend getting either a pose-able figure or a free poser software like DesignDoll or just doing some figure drawing based on tutorials online. Finally, it's apparent that you're going for a manga-esque style, and that's awesome, but don't let dedication style steer you away from what looks "right." What I mean is that in many cases, those who utilize this visual style tend to mangle anatomy at crucial points such as fight scenes or action scenes, creating necks that look strained, arms that look twisted, or shoulders that are way too low on the body (I'm speaking from experience haha).
All in all, you are starting out amazingly well, way better than I was when I first started comics, and I look forward to where you go from here. I hope you'll take my advice, or, better yet, find your own path and make your comic as amazing as possible in your own way.