Feisty looking little fella aint he?

Try cross mixing your colours more...cooler colours in the skin tones to match the wall...warmer colours on the wall (which is waay to monochromatic at the mo)
The anatomy goes a little skew on the legs...i suspect you had good reference for the arms but not the legs!....the legs are also a little soft and airbrushy (is that a word?) compared to the crispness of some of his upper body.

The bricks also look like a filter effect...never a good idea unless it is massively over painted afterwards!

I think you should also be aware that the 'mullet' haircut went out in the 80's and even then was a ghastly fashion mistake!!!!

Haha! Both funny and constructive crit. Thanks Kaduflyer.

Let's try with some general tips:

You can use Andrew Loomis' books to learn more about anatomy.
To learn more about colors you can look at photos and works by great artists. Try to understand why they chose which colors and then try to use the new knowledge for your own work.
Besides that also note how these artists arranged their compositions to get a better feeling for this as well.

However, I see that you already had an improvement with this work here so I'll give you 7 points

"Improvement" on my part means "finally be able to acknowledge the usefullness of photo references." Thanks, Azurelle.