I'm gonna be very critical and judge it harsh, but I will be a positive as possible.
Firstly, it looks too tall for the image. Your player is filling up 3/4 of the height when I feel that it should be near the whole height. This will then help to extend your image sideways and should more in porportion. This is an easy fix, and you will learn about sizing and porportions evantually.
Secondly, it's too red and flat. By that, I mean that it look like it only has two colours and it doesn't obey the rules of threes (Foreground, Midground, Background). This can be fixed in a huge number of ways, eg. brushes, renders, images, textures, shadows, lighting, etc... the list goes on. The best way to improve your skills is by completing a few tutorials. Understand how each step works before moving on to the next. Your energy render placement is probably not the best. It may look like he's on fire, but it doesn't really look firey enough (Fire is Very hard to create, even I have trouble)
As well as those, there is the text, and minor details around the place. I could go on for a while, but that wont be much use to you. So what I do suggest is to look at some tutorials, try out a variety of different images (Even non football ones) and continually post your new works for feedback.
For your first one, that is good.
It is alot better then what mine was.
