wow not bad for 13. You have too many muscles on this guy though. Just study anatomy, and practice drawing muscles. It looks like you've got understructure, and this guy doesn't seem stiff at all. Your main problem is not having a good understanding of the muscles. Draw them from real life, and always try to keep in mind how they connect to the bones, and where they connect to the bones. Plus this guy doesn't seem to have an ear.. Keep practicing, hope I helped!