Similar to what I said in your other thread. I say this, don't try and copy a generalized 'manga' style because there just isn't one. It varies a lot from artist to artist. What I suggest to you rather than just trying to be a 'manga' artist is to take a life drawing class, this will really help you develop your ability to draw the human form and is usually a big help for any artist anyway. From there develop it into your own style which YOU feel comfortable drawing in. It will look and feel a lot less forced to other people and yourself.
To a lot of people 'Manga' is just a means of determining the origin of the comic anyway so what you do would be manga influenced rather than 'manga'. In Japan Manga actually means 'comic'.