Okay before I begin I want to say a few things I saw that you have been working in the digital arts and that you have a real interest in the Sonic art style, I do like your art don't get me wrong on this but I think you should consider doing different art styles, find some artist on DA that you think are amazing and try practicing there styles.
I can't seem to tell what paint software you are using but I recommend practicing in traditional then working your way up to drawing digital.
Now for your proportions, I think you could really improve those skills if you remember these tricks.
Arms should end approximately below the hips of characters, I think you did amazing on the right arm of this character well done! I think you could have added a bit more muscle mass to the arms and keep in mind that two arms on a body are symmetrical to each other.
The elbows should be approximately around where the chest ends and there the stomach starts.
In this drawing if you look that the left arm it looks like the arm is as long as the body.
hands should at least a little bit more that half the size of the head (on a human but I don't know about the Sonic art style...) You should consider practicing human forms every now and then it wont hurt you.... but you can practice what ever you want to!
everything else on this character seams pretty good overall but I do advise you to consider watching art tutorials on YouTube and watching speed paints and studying how those people draw the things YOU want to improve in.
I left a few links that really helped me when I was learning how to draw
Draw With Jazza is one of the YouTubers I HIGHLY recommend he amazing when he explains these tutorials I have been watching this artist for many years now!www.youtube.com/watch?v=XxNUIR…
Proko is also an amazing art teacher if you ever consider doing professional level studies on the human figurewww.youtube.com/user/ProkoTV
I do think you can improve so much if you take my advice but you can go your own way if you would like please let me know what you thought of this critique and let me know if there is anything else I can do to help you!