Adding on Robotacon's list of things to do:
* Work on anatomy(Go use some reference)
* Add more contrast and make a better palette
* Define the light source
* Go get reference(For EVERYTHING)
* Work on a 50% dark gray background
* Try to do as realistic as possible, especially on the portrait(This will help you in the long run if you're into art)
* And honestly, who the hell robs a store half naked? Put some clothes on him