Out of all the works you posted, I feel this one shows the most growth so far.
Some advice I could offer:
1. Try to imagine what shapes build your characters, such as a circle for a head,
rectangles for the chest, and so on.
2. Don't be scared to use references and pull elements of artists that you like.
Do you really like an artist who tends to use large lines? Try applying elements that you like with
your own work.
3. Consider light sources for coloring; In this picture I see some monitors behind the character, which
should imply that there is light behind him. so maybe you could add a little yellow glow on his back.
(Similar to the glow that the "Capcom" screen is emitting).
The most important thing is to keep trying. Even if you don't like something you've created, try and ask "Why?"
If you can answer the question, then you should have the solution to improve!
I hope that helps. Just keep trying and you will improve as long as you still want to!