Ok, I don't want to sound to rude (like I did earlier), so right now the best way to get better is to look at this:
Copy it, and understand what does every line refers to (muscles).
After you're comfy with it, you can try to redo your low poly, but it will take a while to get it. Training is the key. i suggest you to make a thread for that, you will certainly get good advices in the making.