Firstly welcome to the forums. Secondly, I think the first problem here is that your skipping steps. I think you should take a step back(no pun intended) and work on the line art first. Having a nice foundation in the beginning will make things easier. Take it a step at a time. Start from the anatomy and work your way to adding clothes, weapon, colors and more. From there you can decide where you want lights to come from. When lighting the character think of them in simple shapes. Arms would be cylinders. Same with the legs.
As far as what to work on, it would be the fundamentals. Study anatomy, proportions, how folds work and how to light basic shapes.
I did a very simple an quick paintover for the characters anatomy. I didn't do the full body but I hope this still helps. Use reference to finish the rest. If you have a friend that can pose for you or even take a picture of you or them in this pose can help a lot. If not google is your friend.
As far as the colors go, You can always use modifiers like curves, Hue and saturation as well as color balance to adjust what you have.
I don't play league so I don't know anything about this character.
Sorry I had to do this quickly, but again I hope this still helps.
If you need further explanation on something, don't hesitate to ask. When i have more free time I don't mind helping some more. I think this can turn out to be a really cool piece. Look forward to see how to tackle it some more.