This isn't my area of expertise, but I think that I could be of some help. Both my parents are in the design business (Mom has been doing graphic and web design for 18 years and my dad does game design)
I think that if you make the edges a little darker on the dragon (assuming it is a dragon) it will make him pop more. Not in solid black, but just solidify the edges slightly. draw attention to the main focus of the picture. At the bottom jaw of the beast you have a defined outline. Also, add more to the monster. You can't tell what it is really. A dragon? The Devil? I love the concept, but it needs more so people can see what you see in your eyes. Maybe wings or horns. A body would be very helpful in general.
Do the same thing next to the right eye.Same thing with what I'm assuming is a cauldron or flaming rock/fireball. It's not really clear what it's exactly supposed to be. Maybe add some more detail to it. More definition. If it's a rock add some lumps. If it's a cauldron add a handle to it; fireball, some glowing cracks that show the fire within.
You should probably define the background some more so we can tell where he is exactly. In a volcano or Hell (looks like somewhere with a lot of fire). You seem to have a lot of smoke so if you can, do a simple sketch (nothing to detailed) of something like a cave wall behind the smoke.
Outside of these small details I think you did an amazing job! This type of art is something that I look at in awe and would love to do one day myself. The color scheme is great and the lighting is wonderful. Keep up the good work!