Back on the subject:
Start small and use stick figures, from there build on the shapes of muscles and the body, then erase the unnessecary lines and go from there.

But when it comes to manga, I can see that there are relationships between manga and reality. Shapes and form derive from ourselves (even the eyes have a resembelance) which you should always remember, try comparing figures of your drawings with real people. Look at the way your own muscles and body looks and shapes, and work on it from there. Whenever I have trouble drawing hands, i usually just sketch the shape/pose of my own. And remember, you can't rush the picture, the longer you take, the better the results.