What makes manga characters so special? Well, if you already read a manga, you know that most characters have many things in common.
They usually all have big eyes. This is very useful to give the character more emotion, more expression when reacting to a situation.
Manga characters also have tiny mouths. One of the reasons might be that it's easier to animate a tiny mouth in a television series than using a big mouth.
Most old manga movies and TV series were using a very low frame rate to put more emphasis on the character than the action. Manipulating a small mouth was easier back then.
The nose is very often made using a simple and single dot. A very thin line can be drawn from one eye to the top of the nose to help distinguish this one. But the single dot (or small line) is usually more representative of this type of character.
To hold these big eyes, small nose and the tiny mouth, a manga character will need a big round head. The chin is usually pointed and narrow.
The hair of the manga is also very particular.
It can be made with small triangles, long black lines or look more realistic with shades and tones of colors.
The body can come in a variety of shapes, depending to whom the manga is intended. If this one is targeting young people, then chances are that the body will be short and made of rough shapes.
But if the manga is targeting a more mature audience, then the body will have a more realistic (sometimes very realistic) shape.
Of course, these are only rough guidelines that you may follow or not. I don't think that you can find THE absolute blueprint of the perfect manga character anywhere since this medium is evolving very quickly.
But if you are following these basics suggestions, chances are that your creation might look like a manga for someone who's not really familiar with this type of cartoon.
The best thing you could do is read a lot of them, find your favorite one and practice drawing it. But once you start creating your own character, don't try to be a simple copycat. Find and develop your style.
Try mixing some manga particularities (like the big eyes, perhaps the single one available in most mangas!) with your style by creating something new and original.
Everyone can draw manga fan art. Only the best can make this medium evolves. It's up to you to choose where you fit the most!