Hey dude, I looked through your gallery your already very good! But reading through the thread it seems like you want to improve proportions? I actually just started drawing again this month after not drawing for a while. And I found this awesome series on youtube that I think should help you and anyone out a lot. The person who teaches is very talented and very amusing. He goes through the atonomy and proportions of all the parts of people. [link] This is the link to it. It helped me out a lot and hope it helps you out a lot as well. Good luck and keep it, just keep practicing and drawing.
Look up andrew loomis and draw from life. Use photos of real people, objects and animals, stay the hell away from how to draw anime books, and you will improve. If you want to draw anime then fine, but learn proportions and anatomy first before you exaggerate anything.
Start drawing real people. Comics, animated characters, manga, and anime are simplified shortcuts that are made by people who have already studied and understand what the shortcuts represent (at least the good ones have).
You seem to be studying the shortcuts only, so you're not likely to progress further until you put the horse in front of the cart as it were.
Like they say, practice makes perfect. Your not gonna suddenly aquire great artistic abilities overnight. Art takes patience but it also requires that you enjoy what you do and be happy with your own abilities.
You should start out small and look at the small things that you wanna start drawing. Look at references, practice drawing them and master the little things before moving onto the big things.
Also, in regards to drawing manga, I could not recommend a better site than [link]. Its a really wonderful site that helps a lot. Youtube is a great resource as well as DeviantArt.
The best advice I can give to try different techniques and mediums, and to remind yourself that art is supposed to have mistakes one way or another. Artists learn how to improve throughout their whole life.