Great start, nice colours
I don't have much time but a few things that can help make this much better...
Rendering across the whole image has flattened it out.
Obvious examples are that wrinkle on his bicep near his shoulder, and wrinkles in the MC Hammer looking pants.
I'd be inclined to remove all-together that brightest orange on his rear leg and get rid of those horizontal wrinkles where his crotch should be.
Draw perspective lines at a few levels and you'll see his knees are out of perspective - so back knee up and/or foot down.
If his shoulder is supposed to be further back, then darken it more and rotate all the circle things to be a bit more eliptical and remove some of the green bulk on the right side so it is angled back (but leave the edge of the armour there).
On the closer (our left) shoulder, highlight could be a little higher up.
You can bring the head right a bit and bring those teeth up a bit, reduce brightness of top teeth so their in shadow a bit and just make that whole bottom area come up a bit more.
The gun looks cool but I think the barrel bends up a bit at the end and you should render the lighting more from the top, concentrating your highlights accordingly to reduce the flatness.
Feel like editing but no time >.<