This looks good so far. A few things I see.
1.The textures on his clothing, skin, and fire are all the same. Pay attention to surface treatment and how your lighting interacts with it.
2. Give your line/strokes direction. Besides the fire, I see a lot of different flows and strokes going in different directions which in turn makes the illustration a bit muddy.
3.Details. Show a bit more love to the costume design and character's physical appearance. make him stand out. Before you start try to do 4-6 silhouettes and pick from there. This allows your character to have an interesting shape (which you'll build on later)
4. Dead space. Sometimes its okay to do this so this is mostly opinion. to the characters right (our left) I see a warrior hidden. Is he suppose to be hidden? If not, you should bring him out maybe add some trees or mountains.
5. Color. Hmm all I can really say is try to be a bit more vibrant with some things (i.e. the fire and it's lighting) also while working in color check your values. Convert the image to black and white to see if your illustration is just as powerful as it would be with color.
that is all
Keep up the good work