Manga characters are made of basic geometric shapes, the more you know how to put those together in your mind, the better you will be able to draw them.
A good practice to drawing better manga characters is with still life.
1. Draw an egg with all angle, under a single light source.
The egg shape represent the basic shape of the face, once you get the egg shape down and you are able to imagine it in your mind in all angle, you are one step closer being able to do manga face in all angles.
2. Then draw a cone or triangle like shape in all different angles. If you can't find those, get a mug, with handle, and draw it in all different angles, study that shape.
That will be your hint for the manga nose shape changes in all angles.
3. To draw a body in all angles.... find a box, and draw it all different direction. Then move on to drawing boxes in different proportion. Long ones (like the shoe boxes) or square ones, and flatter ones.
4. Study a single T-shirt without anything on it,