[Globu]

Aside from being too smooth? Well, like I said, the first thing *I* would do is find a sprite that can serve as a good example. It may or may not be perfect, but, say, I randomly found 0910_king_of_magma. Then I'd compare what I have to it, and note that the flames in the example sprite tends to use high contrast, not get too dark, and at least some semi-clean lines (again, too much smoothness tends to not fit in right). So I'd pick out some lines of flame and reinforce them, like you can see in the top left section of the flames in the 0910 sprite.

Like I said, I'm not hanging myself out there like an expert. Just giving asked-for feedback and sharing tips I've found useful in my own learning process.